Other major changes:
- pg code now uses only binary format
- pg timestamptz now always UTC (tz = 0), added doc section
- added contracts to most pg "can't-convert" errors
MySQL:
- support multi-packet data rows
- fixed very old length-coding bug (24 vs 32 bit length)
- support large params via long-data packets
- 'any' pseudo-type for parameters
- distinguish 'blob'/'text', 'var-string'/'var-binary'
- read 'text' results as string, not bytes
SQLite3:
- enabled sql types tests
