Original PR was written with 4 spaces instead of 8, do a once off fix
here rather than fixing bit-by bit in the subsequent commits and
cluttering them for review.
This commit adds a chanfitness package which will be used to track
channel health and performance metrics. It adds a channel event
structure which will be used to track channel opens/closes and peer
uptime.
The eventLog implements an uptime function which calcualtes uptime
over a given period and a lifespan function which returns the time
when the log began monitoring the channel and, if the channel is
closed, the time when it stopped moitoring it.
