slt-release-finish,start: gitflow release tools

These tools implement the gitflow release process, auto-generating the
changelog and setting the npm package version.

/to @rmg @bajtos 

I needed to cut a strong-supervisor release that was not from the head of origin/master, unsupported by hubflow, so I finally replaced it with a few lines of shell scripts, as threatened.
Can you extend the output to say:
 - what was done (e.g. what tag was created, which branches were updated)
 - what is next (publish to npmjs, etc.)

The current implementation requires me to manually run the following commands to finish the release:
 - `npm test`
 - `npm publish`
 - `git push ...` (copy-and-paste from the tool output)
 - `git checkout master`

Is there a situation where you don't want to update the origin? Is there a situation when you don't want to update all three entities (tag, production, master) but only some of them? The github flow tool always pushed to the origin, I did not have to worry about which branches to push nor copy-and-paste a git push command to do the push. Why `slt-release` is not doing the push automatically?

As for the releasing to npmjs, can we add a command-line option telling the script to run it automatically for me? Example:

    $ slt-release --publish 1.2.3
    # or
    $ slt-release --npm 1.2.3

(It's ok to do that in a different PR.)