new method to parse header info, shorten GitHub Plugin URI header to owner/repo

Added a new method to parse the GitHub Plugin headers. This should enable an easier transition to the possibility of other repos. Also, shortened the GitHub Plugin URI to only need owner/repo, but allow for full URI if provided.
greatly simplified the return of $git_repo array and other fixes as suggested by @GaryJones
comment on parse_url
Merge pull request #17 from afragen/feature/short-uri

Feature/short uri