history.md does not include info for version 0.8, 0.7.3

[johntrandall]

It is unclear what changed from 0.7.3pre to 0.7.3 and from 0.7.3 to 0.8

[banister]

@johntrandall no features, just bugfixes really. I'll try to update it over the weekend though, thanks for pointing it out