Table field kind fixes

* Bugfix: short-int has kind 'U', not 's'
* Bugfix: kinds 'L' and 'l' were swapped
* Added: short-string kind ('s')
* Deprecated: name UTF8 in favour of LONGSTRING
* Added: nonconformance warning for byte string kind ('x')
* Updated table test accordingly

What's missing is a test case for short strings. I didn't add one as this pre-encoded table thing is a bit scary.