Fix MergeRequests API (ugly fix...)

The GitLab API is inconsistent for merge requests, occasionally using
the singular 'mergerequest' in the url instead of the plural form.
Remove redundant url_params info in specification

Just parse the params out of the url rather than explicitly listing them.
Add support for group membership API calls added in GitLab 6.1

<group>.members(), <group>.add_member(), <group>.delete_member()
Document, expand, and fix sudo usage

Fix bugs with add and find functions.
Add 'with' statement usage.
Added GitLab.find_project_by_name() for new 6.2 API call

Performs a server-side search for projects by project name.
Add new optional User parameters added in GitLab 6.2
Update docs
Add a ChangeLog
Fix regression in Issue.close()
Bump version to v0.5.0