Use edf_set_micro_datarecord_duration when needed

[skjerns]

To circumvent the issues noted here

pyedflib/pyedflib/_extensions/_pyedflib.pyx

Lines 624 to 630 in 0c56f09

	# from the pyedflib documentation:
	# > To avoid rounding errors, the library stores some timevalues in variables
	# > of type long long int. In order not to loose the subsecond precision, all
	# > timevalues have been multiplied by 10000000. This will limit the
	# > timeresolution to 100 nanoSeconds. To calculate the amount of seconds,
	# > divide the timevalue by 10000000 or use the macro EDFLIB_TIME_DIMENSION
	# > which is declared in edflib.h.

we could use edf_set_micro_datarecord_duration instead of edf_set_datarecord_duration when smaller record_durations are requested.

I don't fully understand why these are two different functions yet.
I'm also not sure if the comment is still applicable at the moment.