Use ST_GeomFromEWKT in Geometry bind_expression

By using ST_GeomFromEWKT instead of ST_GeomFromText in bind_expression we allow WKT as well as EWKT bind values.
Add bind_processor to Geometry

This allows using WKTElement objects as bind values.
Add an insertion test

Tests that the Geometry type's bind_expression and bind_processor function work as expected. Also tests that we can work with DBAPI's executemany().