More updates to README.md

The current state of generated docs are in https://github.com/phadej/bacon.js/tree/readme-innerlinks and  http://oleg.fi/bacon-doc/

- every method in `README.md` has an anchor, so you can link to them
- lots of interlinks inside the readme (which are added mostly automatically)
- renamed the second *install* section into *install by npm*
- added description of `observable.onValue`
- added short descriptions of `Bacon.noMore` and `Bacon.more`

I'll try to clean up generator code so it's available as well