Update README.md
Make previous and next work on Overcast.fm

It uses sensible defaults, in line with the iOS app. Previous goes back 15 seconds, while forwards advances 30 seconds.
Merge pull request #72 from vitorgalvao/patch-1

Make previous and next work on Overcast.fm
Added Overcast.fm to the list of supported sites
removed extraneous space from music unlimeted on the readme
Merge pull request #74 from vitorgalvao/overcast-readme

Added Overcast.fm to the list of supported sites
Merge branch 'music-unlimited-space' of github.com:vitorgalvao/beardedspice into vitorgalvao-music-unlimited-space

Conflicts:
	README.md
Merge branch 'vitorgalvao-music-unlimited-space'