Allow parameterized file schemas.

According to section [8.2.4](http://www.steptools.com/library/standard/IS_final_p21e3.html#clause-8-2-4) of the STEP specification, a schema name can be followed by a space-separated list of object identifiers (integers) between braces.

E.g., `FILE_SCHEMA (('AUTOMOTIVE_DESIGN { 1 0 10303 214 3 1 1 }'));`.
