+ Updated `.gitignore`
+ Added `Doxyfile`.
[Doxygen](http://www.doxygen.org) has been setup to look for documented `C` fles within:
+ `src/sodium/includes`; and
+ `test`
When run with the Doxygen tool documentation will be generated within
the directory `doxydoc`. The projects README.markdown file is used at
the documentation's main page.
More information on Doxygen tags and abilities can be found on the
projects website: http://www.doxygen.org
