Created a NANODBC_STRLEN macro so that wide string lengths are properly computed in get_impl.
Reworked last_error to wide strings from SQLGetDiagRec, and convert them (crudely) to narrow strings for the exception message.
Changed the parameter number from "long" to "short" to reflect what SQLBindParameter, etc. expect to see.
added column_size() on the result object
Merge branch 'master' of https://github.com/mcg1969/nanodbc into mcg1969-master
Attempting to merge two different pull requests dealing with unicode.

I've also changed param paramteres to type short as that seems to be the better type. I don't get compiler complaints using longs or shorts, and others do for longs, so the best solution is just to use shorts all the time.

Also took a small but nice bind_parameter() simplification which seems to work fine.

Reverted the date format change.