Include fail statement

Workaround for issue #65
https://github.com/sbadia/puppet-gitlab/issues/65

See https://bugzilla.redhat.com/show_bug.cgi?id=952955 for more information.
[deps] Fix top-scope var. being used without an explicit namespace
[doc] Add info. message about puppet version (refs: #66, closes: #65)
Remove unnecessary inherits

After merge request namespacing all variables, inheriting from the
parent class is no longer necessary.
Combine setup and dependencies classes
Install curl package