Support PostgreSQL 9.3

No changes to the fields are known to have been made, so merely
accepting a new version string suffices.

Add new tests for various version strings.
Update licensing information
Elide exact pg_logfebe version from README

Now that 9.3 is supported the wording is overly awkward for a
first-sentence.  And, it seems self-explanatory enough, it's not like
there are versions of incompatible "pg_logfebe"s around yet.