Simplify the release process

Stop increasing the version in `package.json` after a release, do the change just before the next release.

Add a shell script for making the release in one step.

/to @3y3 please review
/cc @sam-github This is addressing your [comment from Jun 19](https://github.com/node-inspector/node-inspector/commit/79b1d60270e8b2364c2b45510928c442c4c41b78#commitcomment-6737390).
Hmm, what if you are doing a release from a different branch, e.g. `0.6.x`? In which case L29 `git push origin master "$TAG"` won't work too, hmm.

I can add `git pull`, how about that?