Combine multiple printers

[Bungeefan]

I would like to be able to combine multiple printers in any variation and any length.

Example:

You want to prefix your log messages with the log level:
PrefixPrinter → PrettyPrinter

Which could then produce this:

┌──────────────────────────────────────────────
│ 15:20:17.587 (+0:00:00.202000)
├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄
│ 🐛 DEBUG: Test message
└──────────────────────────────────────────────

Or you want to prefix every line:
PrettyPrinter → PrefixPrinter

DEBUG: ┌──────────────────────────────────────────────
DEBUG: │ 15:20:17.587 (+0:00:00.202000)
DEBUG: ├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄
DEBUG: │ 🐛 Test message
DEBUG: └──────────────────────────────────────────────

and so on...

Current blockers:

• Printers take a LogEvent and return a List<String>.

Maybe we should rethink the approach of using List<String>.

[Bungeefan]

Adding feature request by @talhazengin (#22):

PrettyPrinter should have an option to write the log level at the beginning of the log message.

[Bungeefan]

Draft is available under the multiple_printers branch.