'extra_link_args' is for other linker options that do not have their
own first class option, use 'libraries' instead.

Cf. http://docs.python.org/2/distutils/setupscript.html#library-options
Add build instructions that make it more obvious how to supply
setup.py with the necessary paths to header and library files.
Merge pull request #3 from ChristianMC/master

Flesh out build instructions and minor nitpick for setup.py