Support npm script preversion, version, and postversion

[Harris-Miller]

I've begun using this module as a replacement for npm version, but what I'm missing is the auto running npm scripts when I use npm version (a la: https://docs.npmjs.com/cli/version)

Be great if running them could be added in the same order of operation. I'm willing to give that implementation a shot too, let me know if you want me to start investigating

[JamesMessinger]

That's a great idea! I don't have the spare time to implement it right now, but I'll leave this issue open as a to-do item and reminder.

In the meantime, if you want to add this, I'll gladly review a PR. The code already contains an exec() function for running git commands. It shouldn't be too hard to make it run the npm run preversion and npm run postversion commands too.

[webuniverseio]

It is not that easy to use exec to run npm, since on windows it is represented as a .bat file and libuv (that is used by spawn) has a ~1.5 years old bug with .bat and .cmd files... nodejs/node-v0.x-archive#25330, libuv/libuv#358

I'm trying to see how that can be worked around, ideally by avoiding OS sniffing.

[webuniverseio]

Created #17