.sql heuristic falls back to SQL (#4888)
.sql heuristic falls back to SQL (#4888)

* .sql falls back to SQL

- add SQL as fallback for .sql extension.

- SQL PL: add SYSCAT.|SYSPROC.|ASSOCIATE RESULT SET|END\!

- T-SQL: [dbo]

* improve sql heuristics
christop/linguist,github/linguist,christop/linguist,erkyrath/linguist,github/linguist,erkyrath/linguist,github/linguist,erkyrath/linguist,github/linguist,erkyrath/linguist