Add Package.swift and move files around

Sources/Context.swift

@@ -0,0 +1,54 @@
+/// A container for template variables.
+public class Context {
+  var dictionaries:[[String: Any]]
+
+  /// Initialise a Context with a dictionary
+  public init(dictionary:[String: Any]) {
+    dictionaries = [dictionary]
+  }
+
+  /// Initialise an empty Context
+  public init() {
+    dictionaries = []
+  }
+
+  public subscript(key: String) -> Any? {
+    /// Retrieves a variable's value, starting at the current context and going upwards
+    get {
+      for dictionary in Array(dictionaries.reverse()) {
+        if let value = dictionary[key] {
+          return value
+        }
+      }
+
+      return nil
+    }
+
+    /// Set a variable in the current context, deleting the variable if it's nil
+    set(value) {
+      if let dictionary = dictionaries.popLast() {
+        var mutable_dictionary = dictionary
+        mutable_dictionary[key] = value
+        dictionaries.append(mutable_dictionary)
+      }
+    }
+  }
+
+  /// Push a new level into the Context
+  public func push(dictionary: [String: Any]? = nil) {
+    dictionaries.append(dictionary ?? [:])
+  }
+
+  /// Pop the last level off of the Context
+  public func pop() -> [String: Any]? {
+    return dictionaries.popLast()
+  }
+
+  /// Push a new level onto the context for the duration of the execution of the given closure
+  public func push<Result>(dictionary: [String: Any]? = nil, @noescape closure: (() throws -> Result)) rethrows -> Result {
+    push(dictionary)
+    let result = try closure()
+    pop()
+    return result
+  }
+}