I did find the definitions in `PostgreSQL::OID` more readable than these. Maybe add `instance_eval` and get rid of the braces?

```ruby
mapping.instance_eval do
  register_type /char/i,   Type::String.new)
  register_type /binary/i, Type::Binary.new)
  alias_type    /blob/i,   'binary')
  register_type /text/i,   Type::Text.new)
  alias_type    /clob/i,   'text')
  # ...
end
```