Added repo getContributors function.
Added Search API functions.
Started to implement Issues API.

Assignee, event, label and milestone functions are currently unimplemented.
Merge remote-tracking branch 'origin/search-api'
Separate owner and repo for Issue constructor.

It's a bit more useful that way.
Merge remote-tracking branch 'origin/issues-api'
Merge repository-getContributors branch.