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().
Better docs and comments
Comment in tests for WKBElement bind value
InsertionTest class renamed to InsertionORMTest
Add test_WKBElement

This test demonstrates that this works:

obj.geom = WKBElement(...)
session.add(obj)

It works because, in that case, the WKBElement object is not a bind value. It is function call (ST_GeomFromWKB).
Use type_coerce in functional tests
Move test to proper test file
Doc changes for EWKT support
Skip WKBElement test if no shapely
Get ready for 0.2.2
Merge pull request #62 from elemoine/ewkt

Use ST_GeomFromEWKT