Add swift-format (#44)

* Added `swift-format` configuration and applied to entire project.

Adding the following commit hook in `.git/hooks/pre-commit` is
recommended:
``` bash
# swift format changed files
git diff --diff-filter=d --staged --name-only | grep -e '\(.*\).swift$' | while read line; do
    swift-format -m format -i "${line}";
    git add "$line";
done
```

.git-blame-ignore-revs

@@ -0,0 +1,6 @@
+# List of commits to ignore on git-blame.
+#
+# To activate run `git config blame.ignoreRevsFile .git-blame-ignore-revs`
+
+# swift format
+873661ac5bc64f0194a4a0addbc40c2d83d01b50

.swift-format

@@ -0,0 +1,15 @@
+{
+    "version": 1,
+    "indentation": {
+        "spaces": 2
+    },
+    "indentConditionalCompilationBlocks": false,
+    "lineBreakBetweenDeclarationAttributes": false,
+    "lineLength": 200,
+    "multiElementCollectionTrailingCommas": false,
+    "respectsExistingLineBreaks": true,
+    "rules": {
+        "NoAccessLevelOnExtensionDeclaration": false,
+        "UseWhereClausesInForLoops": true
+    }
+}

Package.swift

@@ -3,31 +3,31 @@
 import PackageDescription
 
 let package = Package(
-    name: "ChessKit",
-    platforms: [
-        .iOS(.v13),
-        .macCatalyst(.v13),
-        .macOS(.v10_15),
-        .tvOS(.v13),
-        .watchOS(.v6)
-    ],
-    products: [
-        .library(
-            name: "ChessKit",
-            targets: ["ChessKit"]
-        )
-    ],
-    targets: [
-        .target(
-            name: "ChessKit",
-            dependencies: [],
-            swiftSettings: [
-                .enableExperimentalFeature("StrictConcurrency")
-            ]
-        ),
-        .testTarget(
-            name: "ChessKitTests",
-            dependencies: ["ChessKit"]
-        ),
-    ]
+  name: "ChessKit",
+  platforms: [
+    .iOS(.v13),
+    .macCatalyst(.v13),
+    .macOS(.v10_15),
+    .tvOS(.v13),
+    .watchOS(.v6)
+  ],
+  products: [
+    .library(
+      name: "ChessKit",
+      targets: ["ChessKit"]
+    )
+  ],
+  targets: [
+    .target(
+      name: "ChessKit",
+      dependencies: [],
+      swiftSettings: [
+        .enableExperimentalFeature("StrictConcurrency")
+      ]
+    ),
+    .testTarget(
+      name: "ChessKitTests",
+      dependencies: ["ChessKit"]
+    )
+  ]
 )