Support golang (.go) files

[liujinf]

support golang's comment and metrics.

[adam-waldenberg]

While implementing comments obviously is trivial, the implementation of metrics would have to wait a while, as I am not familiar enough with the Go syntax and I would most likely miss something :).

However, pull requests are always welcome. The metrics system for cyclomatic complexity is very simple and just makes use of a list of entry and exit tokens defined as regular expressions. A short explanation on how to add language support is mentioned in issue #59.

[adam-waldenberg]

Added with #166 - will be merged in 0.5.0.