Add support for inverted sections in the parser

spec/parser_spec.rb

@@ -55,8 +55,8 @@ describe "Parser" do
       with_padding { yield }
     end
 
-    def block
-      pad("BLOCK:")
+    def block(inverse = false)
+      inverse ? pad("INVERSE:") : pad("BLOCK:")
       with_padding { yield }
     end
 
@@ -148,6 +148,18 @@ describe "Parser" do
     end
   end
 
+  it "parses a standalone inverse section" do
+    ast_for("{{^foo}}bar{{/baz}}").should == program do
+      block true do
+        mustache id("foo")
+
+        program do
+          content "bar"
+        end
+      end
+    end
+  end
+
   it "raises if there's a Parse error" do
     lambda { ast_for("{{foo}") }.should   raise_error(V8::JSError, /Parse error on line 1/)
     lambda { ast_for("{{foo &}}")}.should raise_error(V8::JSError, /Parse error on line 1/)