Fixed using spaces in filter expressions and variables lists (#178)

* fixed using spaces in filter expression

* fixed breaking variables lists and filters by spaces

* simplified smartJoin

* avoid force unwrap

Tests/StencilTests/FilterSpec.swift

@@ -78,9 +78,9 @@ func testFilter() {
     }
 
     $0.it("allows whitespace in expression") {
-      let template = Template(templateString: "{{ name | uppercase }}")
-      let result = try template.render(Context(dictionary: ["name": "kyle"]))
-      try expect(result) == "KYLE"
+      let template = Template(templateString: "{{ value | join : \", \" }}")
+      let result = try template.render(Context(dictionary: ["value": ["One", "Two"]]))
+      try expect(result) == "One, Two"
     }
 
     $0.it("throws when you pass arguments to simple filter") {

Tests/StencilTests/ForNodeSpec.swift

@@ -111,8 +111,8 @@ func testForNode() {
         try expect(try node.render(context)) == "empty"
     }
 
-    $0.it("can render a filter") {
-      let templateString = "{% for article in ars|default:articles %}" +
+    $0.it("can render a filter with spaces") {
+      let templateString = "{% for article in ars | default: a, b , articles %}" +
         "- {{ article.title }} by {{ article.author }}.\n" +
         "{% endfor %}\n"
 
@@ -182,7 +182,7 @@ func testForNode() {
     }
 
     $0.it("can iterate over dictionary") {
-      let templateString = "{% for key,value in dict %}" +
+      let templateString = "{% for key, value in dict %}" +
         "{{ key }}: {{ value }}," +
         "{% endfor %}"