Add a "Build" command

[snej]

The "Compile" command (Cmd-K) is only useful for single-file executables. When building a package, or even a multi-file executable, it'll fail with undefined-symbol errors because it only tries to compile the one source file being edited.

A "Build" command that runs "go build" in the current file's directory would be more useful. The sdefresne fork of this repo already has it; hopefully it's easy to move over.

[boggo]

This would be great. While it is not too difficult to have a Terminal window open to compile, it would be nice to do it from within TextMate.