Added licensing documentation to the repository.

This change attempts to clarify the licensing position held by the
PHP-FIG group. To do so it-

1. Assigns the MIT license to code,
2. Assigns the CC-BY 3.0 license to documentation,
3. Provides text of those licenses,
4. Updates the bylaws to express these policies,
5. Updates the "Contributing" document with these policies.
Removed superfluous links to licenses.

Since we're shipping a copy of the licenses this isn't needed.
Removed name/mark usage references.

This issue is more complicated and can be dealt with later.
Minor working changes
Corrected license version, as per mailing list
Merge pull request #202 from tedivm/licensing

Adding licensing documentation to the repository.