Convert the default decay_distributor to a linear distribution
Convert Action#time to a floating-point number, to better support short decay intervals
Different user actions should not be added independently

It leads to clumping around the same action time. Instead they should be added round-robin, and then the anonymous actions should be added on the end, so they are consumed first.
Merge pull request #15 from erikogan/fix-karma-upgrade

Fix karma upgrade