Support google-style custom methods api paths

[mfhellh]

Is your feature request related to one or multiple existing converters?
Affects SpringConverter.

Describe the solution you'd like
Extend SpringConverter to support google-style custom methods api such as /v1/some/resource/name:customVerb. For more info please take a look at their documentation.

As of version 3.3.0, endpoints such as /todos/some:action are parsed as /todos/some}.

Additional context
As a sample of what would the change look like I created pull request #151. PTAL.

Thanks!