Add property based testing

[saatvikshah]

This patch uses hedgehogs property testing framework to validate
timestamp extraction and log merging logic.
Timestamp extraction is checked by ensuring that log lines synthetically
created from a specific timestamp format and timestamp, on applying said
function yield back the originally supplies ts.
Log file merging is similarly checked by generating synthetic log files
of different datetime formats and checking that the timestamps in the
output file are in ascending order.