Sqlacodegen

- Fixed TypeError when inflect could not determine the singular name of a table for a
many-to-1 relationship
- Fixed _IntegerType, _StringType etc. being rendered instead of proper types on MySQL

- Added automatic detection of joined-table inheritance
- Fixed missing class name prefix in primary/secondary joins in relationships
- Instead of wildcard imports, generate explicit imports dynamically (fixes 1)
- Use the inflect library to produce better guesses for table to class name conversion
- Automatically detect Boolean columns based on CheckConstraints
- Skip redundant CheckConstraints for Enum and Boolean columns

- Initial release