Expose SQL Types in Cursor

[celestialorb]

This is a follow-up PR for issue #167, which has had a PR submitted already (#168). When testing this modified pyodbc package locally I found that the coldescription attribute of the cursor was not set properly for procedures that return more than one result set.

[mkleehammer]

Very nice and clean.

I know it seems analogous to Cursor.description, but I am concerned about adding any more processing for something that will be rarely used. When needed it is important, but I think it won't be needed most of the time. What do you think about turning it into a function instead?

It might also be nice to figure out if we can easily make the return type a list of namedtuples. Then we could document that attributes may be added to the tuple in the future, so use the names instead of tuple unpacking.

[mkleehammer]

I've put this on hold for v5 due to the suggestions I made above.