Add bintray release script

I've added a gradle script that sets some properties that are necessary to publish to bintray and then it uses external scripts that make all the magic.

This is the first one: https://gist.github.com/hal9002/0772dffbd8a6a81bc176

This first script uses this other script https://gist.github.com/hal9002/691bbf3340dde3a4591d to generate all the files needed to publish to a maven repo (thanks to @blundell ) and it also sets some basic configuration for bintray and applies the bintray gradle plugin.

The first gist can be modified to allow more customisation if necessary
apache2 where's the shout out :tongue: