Adding users/self/media/liked

[tobystokes]

I added the ability to get the media liked by the authenticated user.
That was my need, I have no idea whether it's of any use in any other use case, so feel free to not pull if you don't think it's of general interest.

[potomak]

Thanks for your work. I'd like to merge this PR, but I think it'd be better to include only changes to README.md and src/instagram.js. I will generate dist/* after the PR get merged and there's no need to include grunt version update.

[tobystokes]

Ah yes of course. I nudged grunt to latest packages because it didn't seem to pull down dependencies right first time, but as you can see, there's very little change that would affect the build.