Rename prefx and prefxes to prefix and prefixes
Fix typo in comment
Implement Exit function.

Later definition of this function will be rewriten to make it possible
to test zfSnap
Convert function names to CamelCase
Write short descriptions of what each function do and simplify IsTure and IsFalse functions
Rename S2Time -> Seconds2TTL, Time2S -> TTL2Seconds
Make OS variable readonly
Add some unit tests