Allow ParsedHashDirectives to have argument types other than strings

[KevinRansom]

ParsedHashDirectives can currently only have string arguments.

This means that the syntax for HashDirectives is constrained to having quoted string arguments.

This makes some of the Hash directive syntax a little clunky.

#time "on"
(* Do lots of stuff here *)
#time "off"

probably would be nicer and perhaps easier to get right first time like this

#time on
(* Do lots of stuff here *)
#time off

Similarly no warn requires numeric error numbers to be integers:

#nowarn "1234" "1235" "99"

Is probably better expressed as:

#nowarn 1234 1235 99

[abelbraaksma]

Hi Kevin, I propose we reopen this in favor of the referenced issue and give this an (albeit trivial) treatment with approval process, RFC etc.

[abelbraaksma]

Here we go. We can keep this closed, but we can continue here (#1368). I hope I captured your intend properly.