Rework tbl(7) layout parsing:

Rework tbl(7) layout parsing:
* Continue parsing even if part of the input is invalid.
* Do not require whitespace between cell specifications.
* Allow tabs as well as blanks between modifiers.
* Mark the 'm' modifier as unsupported.
* Parse and ignore the 'p' and 'v' modifiers.
* Better warning and error messages.
* Get rid of a static buffer.
Improved functionality but minus 50 lines of code.