Added lowercase type converters for all SQL* types

~~Hold off on this for now, as I need to fix a couple of things.~~ Okay now.

* e.g., sqlchar(x) = convert(SQLCHAR, x), etc.
* also: cosmetic changes to ODBC_Types.jl

See line 67 for the type converter change.  

I was finding myself writing converters by hand for the different types, or that I had to keep on looking up the julia type, etc.

This addresses both of those: convenience functions for converting to the types, and formatting the ODBC_Types to make it a little easier to read.