Parameterized enclosing for char and string literals

[bogo8liuk]

charLiteral and stringLiteral lexemes encloses literals, respectively, with characters ' and " (both at the beginning and at the end of a literal) by default. There should be lexemes (one for characters and one for strings) which makes parametric literals enclosing, for instance by taking as arguments a string (not a single character) which encloses a literal at the beginning of it and a string which encloses the literal at the end of it, something like charLiteral :: String -> String -> ParsecT s u m Char. Thus:
charLiteral "<<" ">>" would parse <<c>>, where c is a single character, valid to be a literal character.
This is just an example, before opening a pull request there should be a reasoning about not to make a breaking change (if it's possible).

Anyway, actually, I don't know a clean way to do what I just explained with the actual API.

[phadej]

Both charLiteral and stringLiteral say

The literal character is parsed according to the grammar rules defined in the Haskell report

Breaking change to parsec are not really welcome.