* change bsv file suffix to replay, update strings
* add trivial RPLY block to save states
* WIP rerecording support, doesn't load states properly yet--issue with checking identifiers?
* Fixed a type error to get time identifiers working right, ready for testing
* handle case where state without replay data is loaded during replay
* cleanups
* whitespace cleanup
* Cleanups, change replay file format magic, fix logic around future states
* Remove failed future message
* Add play-replay-from-slot command, fix load-state-from-slot to use given slot
* build fixes
* Fix race conditions in emscripten build and incorrect replay state incrementing
* Style fix for single line if
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Co-authored-by: Joseph C. Osborn <jcoa2018@pomona.edu>