Litle backward incompatibility on token max-age parameter.

max-age replaces olds maxage.
Add long<->bytes transformations to codecs namespace.
Remove String type hint on hmac functions.
Refactored generic signatures namespace.

Changes:
- Improved security with random salt.
- Replace null checking with pure functional monadic error handling.
- Major code and internal api cleaning.
Missing:
- Use key derivation function for key (will be added in very near future)
Add maybe-let macro.
Fix tests.
Remove duplicated and replaced m-maybe macro.

Is replaced by maybe-let macro with more consistent name.
Update changelog changes introduced in previous commits.