Enable lager to use the OTP logger's event pipeline

[Vagabond]

We should really get this finished so let's try to figure out what's missing.

[Vagabond]

Some things we need to do:

• [ ] Documentation
• [x] A way to export the current lager config as a logger config
• [x] An optional way to, in lager:start(), turn the lager config into a logger config programatically
• [ ] Figure out which of the more advanced lager features can still be supported in logger
• [x] Figure out why log events have wrong timestamp
• [ ] Port Lager's disk log internals to make a Logger compatible handler, because disk_log has terrible rotation