This commit add support for enumeration of parallelports.
This is on the base class, as enumeration is platform specific
This function needs to be implemented in derived classes.

…sy-lib into feature/win-parallel-port

PsyTimePoints are BoxedTypes, instead of instances of GObject.
The code related to psy-parallel-trigger still used g_object_unref
on them. This commit will call correctly psy_time_point_free
on them.

fixes #136

Sleep(1), will sleep at least 1 ms on windows, but in practice
it sleeps for much longer e.g. +/- 10 times as long. For timing
stuff accuratly, psylib needs to busyloop until that time arives.
So in order to save energy, psylib sleeps for 1 ms until the
event we are sleeping for is less then 1 ms away, and then it will
start busy looping, until the event-time.

The code in [class.ParallelTrigger] was fine, however, it overslept
because Sleep issue mentionned above. Now TimeBeginPeriod is called
when initializing psylib and TimeEndPeriod is called when deinitialiing
psylib

This fixes #137