The database API for user variables has changed somewhat again, this
time closer to the proper vision. There are now two separate sled
Trees in the Variables struct, one for user-defined variables, and one
for counts. Keys have been changed to be username-first, then room ID.
The signatures of the functions now also use a strongly-typed struct,
UserAndRoom.
As part of this, the Context object now once again avoids allocating
new strings.
Other random changes included here:
- Remove tempfile crate in favor of sled temporary db config.
- Add bincode crate in anticipation of future (de)serializing.
This commit introduces the Sled embedded key-value store for keeping
track of user variables on a per-room basis. Extensive changes were
made to the command module to separate concerns and also pass the
database "connection" down the line.
- A new "Context" object was created to hold information and state
needed for command execution (namely the database).
- Database is very simple for now, storing only user variables.
Refactoring later for storing more complicated types.
- State actor moved into Actors struct, in preparation for either
more actors, or ripping the whole thing out entirely.
- Other modules are also more properly separated, notably
the config module is entirely self-contained.