authors+contributors list

[Graham Percival]

Any new / new-ish contributors, please check:
  http://lilypond.org/website/authors.html

The basic breakdown is:
- if you have git access, you're a developer
- if you don't, you're a contributor
- developers shouldn't appear in the contributor list
- developers can pretty much pick their own title/description/email/web

AFAIK, we haven't been keeping track of this for the past 4-5 months,
so I expect to have a few gaps.

Cheers,
- Graham