Suggestion — R.invert and R.invert.many

I just converted a project of mine from lodash to ramda and couldn't find this function in the docs. If this is already in there, please let me know and I can close this out.

Anyhow, I figured I'd whip something up quickly and see if you guys like it. If you do, I'll write some tests to make it more official. In the mean time I scanned your code and did my best to stick to your coding style — assuming I didn't miss something similar to R.invert — let me know if you'd prefer any code changes.

I think you misunderstood me.

I not only want **ramda.js** to be updated with each commit.  I also want **ramda.min.js** to be updated each time.  I'd rather have everything in the repo in sync.

But if we can get Travis to do this, I think that would be a big win.  I don't know if there's a way to `.gitignore` something so that normal users don't push it but still allow Travis to intentionally push it and yet allow it to be downloaded with a fresh clone.  If so, that's really what I'd like.