feat: Add logger to Zellij

[qepasa]

We add log4rs create for logging across Zellij. Additionally, we capture
stderr output from plugins and log it the same log file as other
Zellij logs.

We set up the logger in zellij-utils/src/logging.rs. The logger parses
configuration from zellij-utils/assets/config/log4rs.yml file. After calling
configure_logger from logging.rs the logger should be available in the
calling thread and all children threads.
Second part of this PR is the mechanism that captures stderr output from
plugins. We setup a customized drain (DecoratingPipe) for plugin
processes in zellij-server/src/wasm_vm.rs. The DecoratingPipe logs the
stderr output from plugins using the same logger as we will use everywhere
else but with custom format.

Implements: #561

Todo:

• (kind of, see comment in DecoratingPipe::flush) make sure we detect byte boundaries correctly in DecoratingPipe::write
• work on log format i.e.: add colors, pad certain parts (looks like there is no way to add colors to file for now)
• cleanup

Note:
I didn't go with slog due to it not being fully compatible with standard rust log::info (warn, err etc.), instead that project prefers to use it's own slog::info (warn, err etc.). I tried to use adapter provided by slog project but it was difficult to share the logger between packages. Slog basically expects you to pass log instance across your codebase, which seems like a lot of effort in case of a project that wasn't initially created with slog usage in mind. Also, there is no official support for adding thread name to log, emitting colored log to file or filtering modules.

Sample from log file:

INFO   |zellij_utils::logging    | 2021-07-13 23:15:16.650 [main      ] [zellij-utils/src/logging.rs:56]: Zellij logger initialized 
INFO   |zellij                   | 2021-07-13 23:15:16.650 [main      ] [src/main.rs:26]: Starting Zellij! 
INFO   |zellij_utils::logging    | 2021-07-13 23:15:16.698 [main      ] [zellij-utils/src/logging.rs:56]: Zellij logger initialized 
INFO   |zellij                   | 2021-07-13 23:15:16.698 [main      ] [src/main.rs:26]: Starting Zellij! 
INFO   |zellij_server            | 2021-07-13 23:15:16.709 [main      ] [zellij-server/src/lib.rs:113]: starts server 
INFO   |zellij_server::wasm_vm   | 2021-07-13 23:15:16.762 [wasm      ] [zellij-server/src/wasm_vm.rs:61]: Wasm main thread starts 
INFO   |tab-bar                  | 2021-07-13 23:15:21.357 [id: 0     ] Creating decorating pipe for plugin: tab-bar! 
DEBUG  |tab-bar                  | 2021-07-13 23:15:21.396 [id: 0     ] [default-plugins/tab-bar/src/main.rs:23] "hello from plugin main :)" = "hello from plugin main :)" 
INFO   |strider                  | 2021-07-13 23:15:27.802 [id: 1     ] Creating decorating pipe for plugin: strider! 
DEBUG  |strider                  | 2021-07-13 23:15:27.843 [id: 1     ] [default-plugins/strider/src/main.rs:8] "hello from plugin main :)" = "hello from plugin main :)" 
DEBUG  |strider                  | 2021-07-13 23:15:27.843 [id: 1     ] [default-plugins/strider/src/main.rs:12] "hello from load2?" = "hello from load2?" 
INFO   |status-bar               | 2021-07-13 23:15:32.170 [id: 2     ] Creating decorating pipe for plugin: status-bar! 
DEBUG  |status-bar               | 2021-07-13 23:15:32.198 [id: 2     ] [default-plugins/status-bar/src/main.rs:22] "hello from plugin main :)" = "hello from plugin main :)" 
DEBUG  |status-bar               | 2021-07-13 23:15:32.199 [id: 2     ] [default-plugins/status-bar/src/main.rs:136] "hello from load" = "hello from load" 
INFO   |zellij_client            | 2021-07-13 23:24:45.110 [main      ] [zellij-client/src/lib.rs:304]: Bye from Zellij! 
INFO   |zellij_utils::logging    | 2021-07-13 23:27:27.729 [main      ] [zellij-utils/src/logging.rs:63]: Zellij logger initialized 
INFO   |zellij                   | 2021-07-13 23:27:27.729 [main      ] [src/main.rs:24]: Starting Zellij! 

[TheLostLambda]

This looks super cool! I'm still a bit homeless at the moment, as I'm between places and moving, but I'll try to give this a look either today or tomorrow! thanks so much for doing this!

Is there anything in particular you'd like me to look at or think about?

[qepasa]

Hey, thanks! For now this is still a bit of WIP, but I think that the general mechanism for plugin logs will not change. Neither will the logging crate (unless you or other contributors suggest otherwise).

As for the initial review, feel free to have a look at it but please remember that it's a bit crude at the moment and might change a bit. I will try to finish it as fast as possible and ping on discord when it's ready for a proper, detailed review. 😃. I added a small guide in the initial comment to make the review as easy as possible.

[TheLostLambda]

Thank you for all of your hard work! This is looking great! I left a couple of comments as a first pass.

The main things I think we should look into are making the plugin log-lines fit with the rest of the log lines (adding a date at least), and writing to the proper Zellij log directory in /tmp.

Overall, I'm very pleased with this!

[TheLostLambda]

I love it! I left a couple of small comments for you to address if you'd like, but I'm happy with merging this! Feel free to do any final cleanup (I'm not sure if you want to keep all of the test messages in?) and merge when ready!

[TheLostLambda]

@qepasa Let me know if you need any help with merge conflicts! I think it's just been a bump in the crate versions though, so it shouldn't be too difficult :)

[qepasa]

@TheLostLambda Done 😃 Also, changed the LoggingPipe::Read to return error as discussed above. Please feel free to merge it

[TheLostLambda]

@qepasa Looks stellar! Thank you for all of your hard work on this! It's been lovely working with you and I'm excited to see you around more!

I'll merge it now and update the changelog!