[grammar] Introduce language grammar for SPARQL

Actually just an empty scope with having source.turtle injected. Used
to have an additional source.sparql scope so that commands and themes
can hook in.
[command] Introduce command for executing SPARQL queries

Pretty cool feature ... it supports magic comments for specifying
SPARQL/SPARUL endpoints against which queries are automagically
executed.  It somehow transforms TextMate into an interactive SPARQL
shell.

https://gist.github.com/peta/1f245dd239e263429236
[command] Enable autocompletion for SPARQL documents

Add support for source.sparql scopes