Hyperlink commits and ranges for arbitrary patterns

[justincampbell]

Idea from #33

[justincampbell]

:commit_url => "http://github.com/cramerdev/capistrano-notifier/commit/%s"
:compare_url => "http://github.com/cramerdev/capistrano-notifier/compare/%s...%s"

"test/%s" % "a" # "test/a"
"test/%s...%s" % ["a", "b"] # "test/test...test"