Feat: Improve log levels (#59)

* feat(Print): Accept the 5 standard log levels

Now the Print function accepts as first argument `-F`, `-E`, `-W`, `-I`,
`-D` to specify the levels Fatal, Error, Warning, Info, and Debug.

* feat(logs): Use Fatal level for Fatal error messages

* refactor(logs): Call Print with semantic level

Use `-I` for info instead of `-1`, `-D` for debug instead of `-2`.

* feat(Print): Optionally prepend log level

If Print is called with a semantic level (F, E, W, I, D), the level will
be prepended to the output. E.g. `Print -W "Something is off"` would
result in "Warn:  Something is off" printed to stderr.

* feat: Use new Print syntax in unfreeze and timeoutpid

Author: alonso-herreros