Allow applications to specify their own logger instance (#3792)
* Support MatrixClient-specific loggers.
Signed-off-by: Patrick Cloke <clokep@patrick.cloke.us>
* Use client-specific logger in client.ts.
Signed-off-by: Patrick Cloke <clokep@patrick.cloke.us>
* Log `fetch` requests to the per-client logger
* Use client-specific logger in rust-crypto