Support RLE mode for samples rates of 50Hz or less. Code from hhermsen
in issue #9.
This is a work in progress. Hopefully RLE can be added for higher
sample rates in the future.
The sample loop was not padded properly in the loop waiting for the
trigger to fire. As a result it was sampling at a much higher rate than
the post trigger sample rate. I've added some delays and padded it out
a bit, it needs further measurement, but is usable now.
