**Breaking changes**
- The random trajectory has been changed slightly to improve handling
of ancient sampling events ({pr}`782`). Thus, simulations for a given
random seed will not be identical to previous versions, if ancient
samples are used.
**New features**
- Automated Docker builds ({user}`agladstein`; {pr}`661`)
- Add mean coalescence time to DemographyDebugger ({user}`petrelharp`; {pr}`779`).
- Improve MassMigration descriptions in DemographyDebugger
({user}`marianne-aspbury`; {pr}`791`).
**Bug fixes**:
- In very, very, very rare cases it was possible to generate a
zero waiting time until the next coalescent event, leading to
zero branch lengths in the output tree sequence and an error
being raised ({user}`molpopgen`, {user}`DL42`, {user}`jeromekelleher`;
{issue}`783`, {pr}`785`).