Extract publish task logic from grunt-gh-pages

[markdalgleish]

Hey Tim. Sorry for the massive pull request, I know how annoying these can be :)

This PR is basically porting all the logic from grunt-gh-pages but removing the dependency on grunt, apart from the utils for now. I've begun trying to port the tests across, but that's going to be a bigger job, so I thought I'd better check in first. There's still lots of work that could be done, but I was hoping to get this into a useable state on npm.

I'm using this work right now in an experimental Gulpfile, in which the deploy task looks like this:

gulp.task('deploy', function(done) {
  ghpages.publish({
    base: path.join(__dirname, 'dist'),
    logger: console.log.bind(console)
  }, done);
});

I'm really keen to help push this over the line so I can use it in my projects, so please let me know if there's anything else I can do to get this onto npm.

[tschaub]

@markdalgleish apologies for the delay in getting back to you on this. It looks great at a glance. I'll try to make some time for a more careful review and then I'll add you as an owner/maintainer.

[markdalgleish]

Great, thank you :)

When you have time, would you be able to help port the tests? I've made a start but it's proving to be quite difficult due to my unfamiliarity with how the original tests hang together. If you port the first one, I'm more than happy to port the rest.

[tschaub]

Thanks for the effort on this @markdalgleish! I really appreciate your help in making this more generally useful. I've added you as an owner/maintainer of the package. I put up a few obvious issues. Let's keep adding more and publish releases as needed.