bug#39663: 27.1; ebnf2ps bugs

[Mattias Engdegård]

A few bugs and other things noticed in ebnf2ps:

* The code resides in lisp/progmodes but isn't actually a mode at all: it 
converts BNF into railway diagrams in Postscript. It looks a bit out of place. 
What about moving it to ELPA?

* Prose values in ABNF don't seem to work. Guilty line:

            (or (looking-at ebnf-abn-non-terminal-letter-chars)

where 'ebnf-abn-non-terminal-letter-chars' is not a regexp but a skip-set used 
in skip-chars-{forward,backward}. This was found by a relint scan.

* Despite a lot of effort been spent on making it work with Latin-1, I get 
UTF-8 mojibake in the PostScript output when using chars in the U+00A0..U+00FF 
range in the rules, eg in nonterminals. Unibyte/multibyte confusion, perhaps?

* The 'ebnf-range-regexp' function is misnamed -- it doesn't return a regexp -- 
and triggers relint's bad-regexp-o-meter. Moreover, it is only there to 
compensate for a bug in Emacs 20, long ago fixed. Calls to the function could 
be replaced by string literals.