renamed the keyMap transformer to keyRename for better clarity

Author: jtnelson

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+#### Version 1.5.0 (TBD)
+* Deprecated `Transformers#keyMap` in favor of `Transformers#keyRename` because the latter is a better semantic representation of what the transformer actaually does.
+* Added `Transformers#keyRename` that takes a single `from` key and a single `to` key and performs the appropriate renaming.
+
 #### Version 1.4.0 (December 24, 2018)
 * Added `Transformers#nest` which takes another `Transformer` and applies it to each level of a nested data structure (e.g. `Map` or `Sequence`).
 * Added `Transformers#copy` which copies the value associated with one key and also associates it with another key.

src/main/java/com/cinchapi/etl/Transformers.java

@@ -211,17 +211,11 @@ public static Transformer keyEnsureCaseFormat(CaseFormat format) {
      * 
      * @param map
      * @return the {@link Transformer}
+     * @deprecated use {@link #keyRename(Map)} instead
      */
+    @Deprecated
     public static Transformer keyMap(Map<String, String> map) {
-        return (key, value) -> {
-            key = map.get(key);
-            if(key != null) {
-                return Transformation.to(key, value);
-            }
-            else {
-                return null;
-            }
-        };
+        return keyRename(map);
     }
 
     /**
@@ -281,6 +275,38 @@ public static Transformer keyRemoveWhitespace() {
         return keyRemoveInvalidChars(Character::isWhitespace);
     }
 
+    /**
+     * Return a {@link Transformer} that renames keys. The renaming rules are
+     * that each key in the provided {@code map} is renamed to its associated
+     * value.
+     * 
+     * @param map
+     * @return the {@link Transformer}
+     */
+    public static Transformer keyRename(Map<String, String> map) {
+        return (key, value) -> {
+            key = map.get(key);
+            if(key != null) {
+                return Transformation.to(key, value);
+            }
+            else {
+                return null;
+            }
+        };
+    }
+
+    /**
+     * Return a {@link Transformer} that renames key {@code from} to the
+     * specified {@code to} key.
+     * 
+     * @param from
+     * @param to
+     * @return the {@link Transformer}
+     */
+    public static Transformer keyRename(String from, String to) {
+        return keyRename(ImmutableMap.of(from, to));
+    }
+
     /**
      * Return a {@link Transformer} that replaces all the character keys in the
      * {@code replacements} mapping with their associated character values in