Add result_descriptions to Rows and Row
Add result_descriptions to Rows and Row

This can be useful for functions that are just passed a `Rows` or `Row`
and want to introspect a bit into the columns.

tempbottle/rust-postgres,tempbottle/rust-postgres,ddrmanxbxfr/rust-postgres,sfackler/rust-postgres,achanda/rust-postgres,achanda/rust-postgres,sfackler/rust-postgres,ddrmanxbxfr/rust-postgres