to_hex() for negative inputs

I only recently realised that to_hex() converts its input to unsigned
before converting it to hex (something that's not mentioned in the
docs):

to_hex(-1) -> ffffffff

I think that's something that some users might find surprising,
especially if they were expecting to be able to use it to output
values that could be read back in, now that we support non-decimal
integer input.

So I think the docs should be a little more explicit about this. I
think the following should suffice:

---
to_hex ( integer ) -> text
to_hex ( bigint ) -> text

Converts the number to its equivalent two's complement hexadecimal
representation.

to_hex(1234) -> 4d2
to_hex(-1234) -> fffffb2e
---

instead of the existing example with 2147483647, which doesn't add much.

I also think it might be useful for it to gain a couple of boolean options:

1). An option to output a signed value (defaulting to false, to
preserve the current two's complement output).

2). An option to output the base prefix "0x" (which comes after the
sign, making it inconvenient for the user to add themselves).

I've also been idly wondering about whether we should have a numeric
variant (for integers only, since non-integers won't necessarily
terminate in hex, aren't accepted as inputs, and don't seem
particularly useful anyway). I don't think two's complement output
makes much sense for numeric, so perhaps it should only have the
prefix option, and always output signed hex strings.

Thoughts?

Regards,
Dean