Add "name" type

This is the type of the datname column in pg_database, which I want so
that I can get a full list of databases. I'm mimicing the text types,
which seems to work, but I'm not sure if it's really the proper way to do it.
Add test for querying datname from pg_database

This is my use case for the "name" type.
Merge pull request #37 from jsanders/add-name-type

Add "name" type