Expose CmdFromDir

[erizocosmico]

Exposes internal functionality of RunFromDir to create a command run from the repo's directory as CmdFromDir.

[AppVeyorBot]

✅ Build vcs build-24.master completed (commit c9a4d75be7 by @erizocosmico)

[dmitshur]

This slightly reminds me of #42. It may or may not be relevant, but I'll mention it here just in case it's helpful to you. See #42 (comment) especially.

[erizocosmico]

Yeah, I guess they're similar. The difference, though, is that with RunFromDir you are already giving the user something to run a custom command, so they might also need access to that command to do something special with it. In #42 what's exposed is a way to get the already defined commands.

For example, in sdboyer/gps#84 it would be impossible doing a fix without access to the *exec.Cmd (using vcs, at least), because you have no control over the command or the process.

[mattfarina]

I like the style of this more than #42. It's more generalized and in a similar vein to RunFromDir.