hash: add missing documentation to all public functions

[nahuakang]

Add missing documentation per v missdoc command for #7047:

$ v missdoc vlib/hash/                                
/home/nahua/projects/v/vlib/hash/wyhash.c.v:10:0:pub fn wyhash_c(key &u8, len u64, seed u64) u64 
/home/nahua/projects/v/vlib/hash/wyhash.c.v:15:0:pub fn wyhash64_c(a u64, b u64) u64 
/home/nahua/projects/v/vlib/hash/wyhash.c.v:20:0:pub fn sum64_string(key string, seed u64) u64 
/home/nahua/projects/v/vlib/hash/wyhash.c.v:25:0:pub fn sum64(key []u8, seed u64) u64 
/home/nahua/projects/v/vlib/hash/wyhash.v:32:0:pub fn wymum(a u64, b u64) u64 
/home/nahua/projects/v/vlib/hash/crc32/crc32.v:48:0:pub fn (c &Crc32) checksum(b []u8) u32 

The following could be updated to #7047:

• vlib/hash/crc32/crc32.v
• vlib/hash/fnv1a/fnv1a.v <- Remove this checkbox
• vlib/hash/wyhash.c.v <- Add this checkbox
• vlib/hash/wyhash.v

Please suggest if my addition can be improved as I only learned about wyhash, CRC-32, etc., today. Cheers!

[spytheman]

Good work.

[larpon]

Looks good to me. I have no idea if "polynomial" is what people usually refer to (I have not personally encountered it in relation to hashing), besides that; nice attention to doc details 👍🏻👍🏻👍🏻

[spytheman]

It is related to the CRC32 calculation, see https://en.wikipedia.org/wiki/Cyclic_redundancy_check .