Add support for uuid::Uuid

[vnghia]

Close #33

[finnbear]

Thanks for the PR! Here are a few thoughts:

• I'm in favor of accepting this impl if uuid doesn't want to derive it 👍
• The binary representation you chose differs from Add bitcode support uuid-rs/uuid#739. Theirs encodes a [u8; 16] whereas yours encodes a u128. There may be an alignment difference and, for that and other reasons, performance difference. I'll personally benchmark this before merging.
• I'd like to use the strategy I used in Add support for std::net::{*Addr*} #30 to avoid writing custom code each time we need to encode one type in terms of another. That's not reviewed/merged yet so this will have to wait.

[vnghia]

Hi @finnbear, I use the new approach as you mentioned. Essentially just move ConvertFrom related code to a new mod and use that for encode/decode uuid. I let you decide which binary representation to go (u128 vs [u8;16]) but I think it is done on my side.

[finnbear]

Thanks for this! Regarding the encoding process, @caibear has recently started experimenting with using uuid's support for bytemuck to make it more efficient than what I suggested. I'll keep you updated :)