* Removed ‘optionMaybe’ parser, because ‘optional’ from
‘Control.Applicative’ does the same thing.
* Renamed ‘tokenPrim’ → ‘token’, removed old ‘token’, because
‘tokenPrim’ is more general and ‘token’ is little used.
* Fixed bug with ‘notFollowedBy’ always succeeded with parsers that
don't consume input, see #6.
* Hint system introduced that greatly improved quality of error messages
and made code of ‘Text.Megaparsec.Prim’ a lot clearer.
The improvements affected other modules too:
* Some parsers from ‘Text.Megaparsec.Combinators’ now live in
‘Text.Megaparsec.Prim’.
* Hint system improved error messages, so I needed to rewrite test for
‘Text.Megaparsec.Char.eol’, since it's error messages are very
intelligent now and cannot be emulated by ‘newline’ and ‘crlf’ parsers
used separately.
* Test for Bug9 from old-tests is passed successfully again.
