Use GitHub Release API to create and upload built browser files

[mde]

Add steps to the Jake PublishTask to do this automatically as part of the build.

[TimothyGu]

Grunt has https://github.com/geddski/grunt-release and https://github.com/atom/node-github-releases. Maybe switch to Grunt?

[mde]

I am admittedly biased because I wrote Jake, but I kind of hate Grunt. :) I don't really mind Gulp, because the task API is exactly the same as Jake's, but I do think all the streaming is pretty gratuitous in a build tool.

The PublishTask can take a simple function for additional publish steps, or we can build a prereq task (again, a simple function) which does this.