Added support for composer.lock files.
Upgraded test suite to support duplicating tests for different sources.

This change allows for easier testing of different sources of
information- specifically composer.lock as well as installed.json. It
does this by taking the existing tests, abstracting them out, and then
creating source specific tests that extend off of them.
Merge pull request #3 from tedivm/composer_lock

Add support for reading composer.lock file.