Cleaned up sparql-get-format to remove multiple if statements.
SPARQL query now sent as post form data as per the SPARQL spec.

There is a strong convention to send the query as a url parameter, but
I'm prety sure that it's only a convention.
Allows the user to choose output formats, including "Custom".

The custom string included to support strange endpoints with bizzare
non-spec output formats (if there are any such servers).