Remove internal "arguments" terminology

The original version of much of the interal Brief documentation used
"argument(s)" to refer to data stored on the Brief. This was influenced
by some of the original intent, but I've come to feel that--especially
with the introduction of more callables--this terminology serves only to
confuse the documentation.

Hence I have switched to using, simply, "data" to describe the data
stored in a Brief, and "store" to refer to the location where that data
is stored.

src/Brief.php

@@ -7,14 +7,14 @@ class Brief
      *
      * @var array
      */
-    private $arguments = [];
+    private $store = [];
 
     /**
      * A limited list of terms that cannot be used as argument keys.
      *
      * @var array|object
      */
-    static $protected = ['protected', 'arguments', 'aliases', 'logger'];
+    static $protected = ['protected', 'store', 'aliases', 'logger', 'callables'];
 
     /**
      * An array of aliases for internal terms. The key is the alias; the value 
@@ -251,7 +251,7 @@ protected function storeSingle($value, string $key = null, int $order = null): s
             $key = $this->getAuthoritativeName($key) ?? $key;
         }
 
-        $this->arguments[$key] = [
+        $this->store[$key] = [
             'value' => $value,
             'order' => $order
         ];
@@ -303,7 +303,7 @@ public static function isKeyAllowed($key)
      */
     public function __isset($name)
     {
-        return in_array($name, array_keys($this->arguments));
+        return in_array($name, array_keys($this->store));
     }
 
     /**
@@ -342,8 +342,8 @@ public function __set(string $name, $value)
      */
     protected function getArgument($name)
     {
-        return isset($this->arguments[$name])
-            ? $this->getValue($this->arguments[$name])
+        return isset($this->store[$name])
+            ? $this->getValue($this->store[$name])
             : null;
     }
 
@@ -361,7 +361,7 @@ protected function getArgument($name)
      */
     protected function getAuthoritativeName($name)
     {
-        if (isset($this->arguments[$name])) {
+        if (isset($this->store[$name])) {
             return $name;
         }
 
@@ -388,9 +388,9 @@ protected function getValue($item)
      *
      * @return array
      */
-    protected function getArgumentsSortedByOrder()
+    protected function getDataSortedByOrder()
     {
-        $rekeyed = array_column($this->arguments, null, 'order');
+        $rekeyed = array_column($this->store, null, 'order');
         ksort($rekeyed);
 
         return $rekeyed;
@@ -408,7 +408,7 @@ protected function getArgumentsSortedByOrder()
      */
     protected function getOrderLimit(string $which = 'start', string $attribute = null)
     {
-        $ordered = $this->getArgumentsSortedByOrder();
+        $ordered = $this->getDataSortedByOrder();
         if ('start' === $which) {
             $limit = reset($ordered);
         } else { // i.e. 'end'
@@ -462,7 +462,7 @@ protected function getIncrementedOrder(): int
      */
     protected function getFilledOrdered($fill = null)
     {
-        $orders = $this->getArgumentsSortedByOrder();
+        $orders = $this->getDataSortedByOrder();
 
         return array_map(function ($key) use ($orders, $fill) {
             return $orders[$key] ?? ['order' => $key, 'value' => $fill];
@@ -483,21 +483,21 @@ public function getOrdered($fill = null)
     }
 
     /**
-     * Get all arguments in this Brief as a keyed array.
+     * Get all data in this Brief as a keyed array.
      *
      * @return array
      */
     public function getKeyed()
     {
         return array_map(function ($block) {
             return $block['value'];
-        }, $this->arguments);
+        }, $this->store);
     }
 
     /**
      * Pass an unmodified Brief to an callable.
      *
-     * If the callable does not understand Briefs or how to get arguments from 
+     * If the callable does not understand Briefs or how to get properties from 
      * objects, you should probably use `pass()` instead.
      *
      * @param callable $callable
@@ -510,7 +510,7 @@ public function debrief(callable $callable)
     }
 
     /**
-     * Pass the contents of a Brief as a series of arguments to callable.
+     * Pass the contents of a Brief as a series of arguments to a callable.
      *
      * This method allows for Brief to easily interact with methods that do not 
      * know how to handle it specifically.
@@ -578,8 +578,8 @@ public function find($keys)
     /**
      * Call a callable on each item of this Brief.
      *
-     * This is method is intended for use with keyed arguments. Ordered
-     * arguments may produce strange results.
+     * This is method is intended for use with keyed data. Ordered
+     * data may produce strange results.
      *
      * This acts directly on the Brief on which it is called, and returns that
      * Brief. Be careful; this means that your original Brief is changed. If 
@@ -601,8 +601,8 @@ public function transform(callable $callable)
     /**
      * Call a callable on each item of a copy of this Brief.
      *
-     * This is method is intended for use with keyed arguments. Ordered
-     * arguments may produce strange results.
+     * This is method is intended for use with keyed data. Ordered
+     * data may produce strange results.
      *
      * This acts on a copy of the Brief on which it is called, and returns the
      * new Brief, leaving the original unmodified. If you don't want this
@@ -690,7 +690,7 @@ public function log(string $name, string $description = null, array $data = [])
     public function export()
     {
         return [
-            'arguments' => $this->arguments,
+            'store' => $this->store,
             'aliases'   => $this->aliases,
             'callables' => $this->callables,
         ];
@@ -710,11 +710,11 @@ public function export()
     protected function import(Brief $items, $settings)
     {
         [
-            'arguments' => $arguments,
+            'store' => $store,
             'aliases'   => $aliases,
             'callables' => $callables
         ] = $items->export();
-        $this->arguments = $arguments;
+        $this->store = $store;
         $this->aliases   = $aliases;
         $this->callables = $callables;
         if (is_array($settings) && count($settings) > 0) {