Add python wrapper classes for generating javascript

I added some classes for generating javascript strings: `Function` corresponds to function which can has chainable calls, `AnnoymousFunction` corresponds to `function(x) { y }`, `Assignment` generates `var x = y`, but all of them have no indentions.

If the project use jinja2 or other templates engines, I do not think they can be well tested, so I try to add these functions.