Linkify Github usernames in authors list

- Linkify github usernames
- Remove usernames that do not exist

Change-Id: Ib88b70a3010e915b3570ae5062c8cb416c9a6462
Add links to Twitter accounts

Change-Id: Ic88eb128384b3cc9108151c219cd759c7524a4f1
Merge pull request #2140 from dpursehouse/linkify-usernames

Linkify Github usernames in authors list