Dio extension

See merge request !4

MONOTONIC will provide better stats in the short term as we have no NTP adjustment but the internal oscillator of the PC will slowly drift and then the statistics will be worst.
REALTIME as a worst variance, but it will be always in sync. The user should also take into account that WR and host time should be properly syncrhonized to NTP in order to get comprehensive (below 1s) mean/min/max values.

Delete WR_DIO_F_WAIT flag when flushing FIFOs

Now, a timeout can be specified to block until new events reach a single channel
or the specific timeout expires.

If get_utc_ts_from_fmc_dio_device returns EAGAIN, we have to check later because
there are not more timestamps (Other errors cause an exit).

It helps to identify the number of times that run() function is called for the
stats-engine. This is useful just to compare with the number of timestamps received.