Add clint for checking coding style

Adding a lint script for checking source files for coding style.

The new neovim coding style, as decided in the poll in #104, is a modification of the [Google C++ coding style](http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml) with the following modifications:

 * Function names are `lower_case` rather than `PascalCase`
 * Struct and enum names that have not been typedef-ed are `struct lower_case` and `enum lower_case`.
 * Opening braces for functions appear on the next line.

This PR is for adding Google's cpplint.py lint script and modifying it with the above changes. We will also do some trial conversions of some source files to determine whether additional tweaks are required. Due to the additional time required to make modifications to cpplint.py, these additional tweaks should be limited and in favor of adhering more closely to the Google convention than diverging from it.