Conversions between Rust and Postgres types for rust-postgres

Supports conversions for the following postgres types:

• Box
• Cidr
• Circle
• Hstore
• Interval
• Line
• Lsn
• Mac address
• Path
• Point
• Polygon
• Range
• Snapshot
• Timetz
• TsQuery
• TsVector
• Xid
• Xml