feat(context): Add flatten method

docs/api/context.rst

@@ -0,0 +1,51 @@
+Context
+=======
+
+A Context is a structure containing any templates you would like to use in a
+template. It’s somewhat like a dictionary, however you can push and pop to
+scope variables. So that means that when iterating over a for loop, you can
+push a new scope into the context to store any variables local to the scope.
+
+You can initialise a ``Context`` with a ``Dictionary``.
+
+.. code-block:: swift
+
+    Context(dictionary: [String: Any]? = nil)
+
+API
+----
+
+Subscripting
+~~~~~~~~~~~~
+
+You can use subscripting to get and set values from the context.
+
+.. code-block:: swift
+
+    context["key"] = value
+    let value = context["key"]
+
+``push()``
+~~~~~~~~~~
+
+A ``Context`` is a stack. You can push a new level onto the ``Context`` so that
+modifications can easily be poped off. This is useful for isolating mutations
+into scope of a template tag. Such as ``{% if %}`` and ``{% for %}`` tags.
+
+.. code-block:: swift
+
+    context.push(["name": "example"]) {
+        // context contains name which is `example`.
+    }
+
+    // name is popped off the context after the duration of the closure.
+
+``flatten()``
+~~~~~~~~~~~~~
+
+Using ``flatten()`` method you can get whole ``Context`` stack as one
+dictionary including all variables.
+
+.. code-block:: swift
+
+    let dictionary = context.flatten()