Lise

* Fix the rest of the loader

* Fix a loading error when you make two keyframes and then start the engine before the first

* Seek bar for time travel in ELiDE, and some other minor UI improvements
* Vastly improved performance in ELiDE for large worlds
* History queries no longer require the whole of history to be loaded, and are faster
* SQLAlchemy is now a hard dependency
* numpy is required again
* Save the state of the randomizer every time you use it, not just on time travel
* Rule stepper now works when you reopen the sim
* New example sim, wolfsheep.py
* `enforce_end_of_time` option, so it's not so trivial to make voids of time by accident
* Lots of crash fixes
* yapf formatting, with tabs
* Improved documentation

* Fix an intermittent error where entity deletion sometimes wouldn't go through all the way
* Performance improvements
* LiSE now saves keyframes on close by default. Change ``keyframe_on_close`` to ``False`` to disable this
* Renamed "modulus" options to end with "interval" instead
* Disable the cache arranger by default

* ELiDE now has the Timestream view, easing time travel when history gets complicated
* Rename "avatar" to "unit"
* Nodes now support the `.user.only` property, just like characters' `.unit.only`
* Improve interprocess communication some more, particularly when time travelling between branches
* Tab indentation, with yapf formatting
* Rename some Engine methods to use snake_case
* numpy is no longer required for the LiSE core (will speed up IPC, though)
* Fix a loading error with changes in branches other than trunk
* Crash fixes
* Drop support for Python 3.6

* Optimize interprocess synchronization
* Fix some inconsistencies in the rulebook sync
* Crush all of a character's initial state into the one keyframe, fixing integrity problems
* License change; no longer accept later versions of the AGPL
* Support networkx 2.5
* ELiDE changes
* Rule stepper to help you view the state of the game after one rule's run, just before the next
* Don't crash when resuming the game on non-trunk branches
* Fix stats configurator
* Fix rules configurators
* Accept a prefix on the command line
* Grid view shows characters other than the one you started with
* Dialog options from the game itself don't appear more than requested
* Fix crash when laying out one-dimensional boards