New readme

Mostly a rearrangement of the old one.

Changes, amongst others:
List of bindings with internal links to details
section for details for every library
moved derelict 1&2 info to the bottom, with a link from the top.

It's clearer as to what the project offers while still being explicit about it being an alpha.

This would probably need filling out a bit (particularly the package sections) before merging.