Use syntax-propertize-function

[gracjan]

Emacs 24 and later has syntax-propertize-function that can put non-default text properties on characters in a buffer depending on context they appear in. This is needed to properly handle apostrophe in its many usages (#549) and could simplify other cases like:

• a dash sometimes starting a comment
• a backslash inside strings and gap rule

For now haskell-mode uses old mechanism of font-lock-syntactic-keywords that is not expressive enough to handle Haskell cases. Dropping font-lock-syntactic-keywords means dropping Emacs 23 support as Emacs 23 does not have syntax-propertize-function.