Make ctors that accept slices infallible using arrays and other breaking changes

[KodrAus]

Closes #150 #459 #329 #533

Infallible array inputs

This is a breaking change that changes &[u8] inputs to Uuid methods to &[u8; N]. This lets us make these methods infallible so they can be used in other const functions. If a caller only has a &[u8] to pass in, they can use try_into to convert it into a &[u8; N].

Infallible variant

It's not possible for the variant to ever return None, so we don't need to return an Option for it.

Compact serializer by default

We now serialize a 16 element tuple instead of a slice of bytes in non-human-readable formats.

[KodrAus]

While working on this I've also catalogued our unstable dependencies. I think the only public one left is winapi, which is unlikely to change in a hurry, but we should consider shifting it out into an external library that just offers two functions:

pub fn uuid_from_guid(guid: Guid) -> Uuid;

pub fn guid_from_uuid(uuid: Uuid) -> Guid;