Review portable storage implementation.

[jeandudey]

Checklist:

• [x] Do this implementation binary output matches the one in Monero's epee?
• [x] Add test's to verify this it's compatible with Monero.
• [x] Also, do this implementation follow the same semantics found in Monero (how portable storage sections are created)?
• [x] Do types have good names that reason about theri meaning?
  • [x] WTF is ToUnderlying?, explore an approach using std library.
• [x] Is it using failure optimally?
• [x] Review Bytes and BufMut usage.
• [ ] Test the parser never crashes.