No testing has been performed yet, but changes are extensive enough to
warrant a commit. Of particular note:
- SQL states are enumerated in a separate trait to reduce duplication
- PDOStatement is now an abstract class to avoid duplication of
engine-specific error handling
- Error handling has been cleaned up somewhat
PDO does not adequately inform PostgreSQL of a parameter's type, so type
casts are required. Rather than adding these to each query manually, the
queries are instead processed to add type hints automatically.
Unfortunately the queries are processed rather naively; question-mark
characters in string constants, identifiers, regex patterns, or geometry
operators will break things spectacularly.
