Fix/issue 9

[omibo]

Add documentation for keccakf.rs and aux_functions.rs. Specifically:

keccakf.rs:

• rotate_left64() function.
• keccakf_1600 function.

aux_functions.rs:

• nist_800_185 module
• byte_utils module

[Dustin-Ray]

thanks for the effort on this. The original objective of #9 is to find anything that is undocumented and provide documentation if it makes sense to do so. Much of this PR is modifying existing docs which isnt really needed at this time.

the area that needs the most help right now would be here, anything that is pub will be publicly exposed and should have docs explaining its usage.