Transitioning documentation to PEP 257 style format

I went ahead and started to transition some of the documentation over to the [PEP 257](http://legacy.python.org/dev/peps/pep-0257/) format, specifically the [NumPy/Scipy style](https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt). I also added some installation, licensing, and dependency information to the README. The work is only partially complete because I didn't want to invest too much time if this something that you do not prefer. 

The desired result, at least in my mind, is to have sphinx generating the documentation ([readthedocs](https://readthedocs.org/) integration would be especially nice) with the README containing only an introduction and the installation type information.

Best,
-tamas 
If you wish to perform weighted algorithms, such as weighted viterbi, you need to specify the weight each state has. Instead of making a new method for the weighted algorithms, it seemed easier to just make the weight a property of the state, which defaulted to 0 when you wished the unweighted versions of algorithms.