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.
I don't know how closely dash follows the letter of posix, but the bash man page is so enormous, I get all my scripting help from `man dash` now-a-days, its nice and easy to read, and hopefully keeps my shell code reasonably portable.