Refactored MakeWinMsgEv slightly to remove ctrl variable

Another one bites the dust...getting very close to a clean MakeWinMsgEv!
Updated winmsg.{c,h} copyright to include my changes
Initial grammar in EBNF for winmsg
Corrected optional rend attrmod nonterminal (not rend attrchtype) in EBNF grammar
Typo correction in winmsg EBNF for escchar in literal nonterminal
Removing `l' in `rend attrvalue' nonterminal; keeping `B' for backwards compatibility

After discussing with Amadeusz, he is okay with restoring the original `B' and
dropping `l'.
Added `.' as a valid character for escflag

Will be used to represent percentages where they must be disambiguated from
other numerical values (e.g. %[).
Added escfmt support to winmsg grammar

Amadeusz described an example to be %W, where %W would use the default
format and %W{...} would provide a custom format `...' to use for each
window---a foreach, almost.
Began test-driven development of winmsg lexer