Fix typo and $PID example in README
Update README.md
Fix example.
Fix header guards (fixes #2).

TIL: Leading underscores followed by a capital letter is
actually a reserved identifier. This replaces the header
guards with a non-reserved identifier.
Fix error setting env variable HYPTIME_UNLINK to None
Remove short arguments support
Assign 'true' or 'false' to HUPTIME_MULTI