Logging enhancements and cleanup (#2502)

* Logging enhancements and cleanup

- Removed debug log messages every time `Config.get_conf` is used or a JSON file is read/saved. The basic configuration is now logged once with DEBUG when the bot starts up instead.
- Changed logging output format to reverse date order, include seconds, and use the logger's name instead of the module, function and line number.
- Log files are now kept in the `DATAPATH/core/logs` directory. Each time Red is restarted, a new log is created, and the old ones renamed in a rotating fashion. There can be a maximum of 9 logs in total.
- Each log file now has a smaller max size of 500KB before it will be split into multiple parts. There are also a maximum of 9 parts of each log.
- Discord.py logger now uses the same output formatter as red's loggers
- Moved logging setup code into `redbot.logging` module.

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

* Reformat

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

* Implement discussed changes

- We maintain a red.log over multiple runtimes, alongside a latest.log and previous.log for individual runtimes.
- Naming convention changed a bit. E.g. when latest.log is just one part, it will be named latest.log. When it becomes two parts, they will both be named latest-part1.log and latest-part2.log.
- Rotation direction is reversed. This means as the files end up being named in chronological order.

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

redbot/core/cli.py

@@ -1,5 +1,6 @@
 import argparse
 import asyncio
+import logging
 
 
 def confirm(m=""):
@@ -97,7 +98,14 @@ def parse_cli_flags(args):
         "login. This is useful for testing the boot "
         "process.",
     )
-    parser.add_argument("--debug", action="store_true", help="Sets the loggers level as debug")
+    parser.add_argument(
+        "--debug",
+        action="store_const",
+        dest="logging_level",
+        const=logging.DEBUG,
+        default=logging.INFO,
+        help="Sets the loggers level as debug",
+    )
     parser.add_argument("--dev", action="store_true", help="Enables developer mode")
     parser.add_argument(
         "--mentionable",