Update docs for ‘charLiteral’ to mention ‘\&’

Close #154.

Text/Megaparsec/Lexer.hs

@@ -361,6 +361,14 @@ lineFold sc action =
 -- string literals:
 --
 -- > stringLiteral = char '"' >> manyTill L.charLiteral (char '"')
+--
+-- If you want to write @stringLiteral@ that adheres to the Haskell report
+-- though, you'll need to take care of the @\\&@ combination which is not a
+-- character, but can be used to separate characters (as in @\"\\291\\&4\"@
+-- which is two characters long):
+--
+-- > stringLiteral = catMaybes <$> (char '"' >> manyTill ch (char '"'))
+-- >   where ch = (Just <$> L.charLiteral) <|> (Nothing <$ string "\\&")
 
 charLiteral :: (MonadParsec e s m, Token s ~ Char) => m Char
 charLiteral = label "literal character" $ do