Add basic support for ranges in for loops

Closes kylef/Stencil#128

Sources/ForTag.swift

@@ -90,6 +90,10 @@ class ForNode : NodeType {
       values = dictionary.map { ($0.key, $0.value) }
     } else if let array = resolved as? [Any] {
       values = array
+    } else if let range = resolved as? CountableClosedRange<Int> {
+      values = Array(range)
+    } else if let range = resolved as? CountableRange<Int> {
+      values = Array(range)
     } else {
       values = []
     }

Tests/StencilTests/ForNodeSpec.swift

@@ -37,6 +37,22 @@ func testForNode() {
       try expect(try node.render(any_context)) == "123"
     }
 
+    $0.it("renders a context variable of type CountableClosedRange<Int>") {
+      let context = Context(dictionary: ["range": 1...3])
+      let nodes: [NodeType] = [VariableNode(variable: "item")]
+      let node = ForNode(resolvable: Variable("range"), loopVariables: ["item"], nodes: nodes, emptyNodes: [])
+
+      try expect(try node.render(context)) == "123"
+    }
+
+    $0.it("renders a context variable of type CountableRange<Int>") {
+      let context = Context(dictionary: ["range": 1..<4])
+      let nodes: [NodeType] = [VariableNode(variable: "item")]
+      let node = ForNode(resolvable: Variable("range"), loopVariables: ["item"], nodes: nodes, emptyNodes: [])
+
+      try expect(try node.render(context)) == "123"
+    }
+
 #if os(OSX)
     $0.it("renders a context variable of type NSArray") {
       let nsarray_context = Context(dictionary: [