Add support for running go generate

[mdwhatcott]

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[jbuberel]

@mdwhatcott If you have a few minutes, take a look at the suggested configuration for running benchmarks described here:

https://github.com/golang/sublime-build/issues/13

Could you give that approach a try?

I could also use a couple of example go generate commands that you typically run. Would you mind pasting a few here?