I wanted to use the Target::Pipe feature of env_logger so that we could
log to a log file as well as stderr, but it just doesn't work
(https://github.com/env-logger-rs/env_logger/issues/208).
Since we were already composing over the top of the logger in order
to capture data for our ringlog, this commit embraces that and makes
our logger responsible for both stderr and log file printing.
Thankfully, we can use the filter parsing code from env_logger to
avoid having to get too crazy with this.
Logs are stored in the runtime directory and look something like:
/run/user/1000/wezterm/wezterm-gui-log-596324.txt
Logs are collected on all platforms.
There isn't currently a thing to clean up logs.
