Use Ruby's require_relative to load project specific libraries.

By using require_relative, we can run cpc and spec tests without
having to be in a certain directory.  The require_relative method
was added in Ruby 1.9.2.

See https://practicingruby.com/articles/ways-to-load-code?u=dc2ab0f9bb
and http://extensions.rubyforge.org/rdoc/classes/Kernel.html