Add coding guidelines

These are the coding guidelines as updated from what originally was in
PyCogent. I took a pass through the document and updated where I saw fit,
however I know that people will like to add things that are currently not being
covered, so let me know and I'll add/change as needed.

The section that needs the most attention is the testing section. I updated it
but I know there might still be things that are missing as I'm not super
familiar with nose.

I've also added a minimal section about git that mainly points to other well
known and well written git guides.

Fixes #272
Not sure but to avoid any confusion, I'll change the name of the class
to Numbers.
On (Jun-10-14|11:48), Greg Caporaso wrote:
> > +^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > +
> > +The structure of your module should be similar to the example bellow, note that scikit-bio uses the `NumPy doc`_ standard for documentation, `this document explains`_ how to do this:
> > +
> > +.. _`NumPy doc`: https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt
> > +.. _`this document explains`: https://github.com/biocore/scikit-bio/blob/master/doc/README.md
> > +
> > +.. code-block:: python
> > +
> > +    r"""
> > +    Number List (:mod:`skbio.core.numbers`)
> > +    =======================================
> > +
> > +    .. currentmodule:: skbio.core.numbers
> > +
> > +    NumberList holds a sequence of numbers, and defines several statistical
> 
> This example kind of contradicts the suggestion above, which says not to include the type in the name, but maybe that is only relevant for variables (not classes)? 
> 
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> https://github.com/biocore/scikit-bio/pull/401/files#r13611588