Implement string (partial) and operator modules

* Implements part of the [string module](http://docs.python.org/2.6/library/string.html) in the standard library. I didn't implement any of the formatting stuff, and I also didn't implement any of the deprecated functions. The module documentation states that those deprecated methods should be avoided in favor of using the methods defined on the str standard type.

* Implements a large part of the [operator module](http://docs.python.org/2.6/library/operator.html) in the standard library. I did leave a few unimplemented because I didn't see an easy to way to do so - let me know if I'm missing anything obvious!  
    - Examples of ones I skipped include `operator.not_()` and `operator.index()`
    - I also skipped the inplace versions of the operator functions. It looks like most places in Skulpt just map the inplace operation to the non-inplace version (e.g. in `number.js:571`)


The unit test suite seems to pass, but let me know if you have any questions or if I've missed anything. (In fact, I'm expecting to have missed stuff - I generally did stuff the first way I figured out how to, not necessarily the right way!)