Refactor logging

[adamcharnock]

Lightbus' logging system needs a major refactoring, or perhaps completely tearing our and reimplementing. It was one of the first areas implemented and I've been papering over the cracks since then.

I've marked this as a 'good first issue', but the caveat being that you'll need a decent understanding of Python's logging system.

Existing problems

• Cannot use placeholders in log messages (e.g. %). This means all messages must be formatted strings, regardless of whether the message will be logged or not. This impacts performance.

Existing features (to keep)

I want the following (currently existing) features to also be present in the new system:

• Coloured output based on log level (TTY only)
• Emoji output (TTY only) – May sound silly, but this has really helped me scan through the logging output
• Bold text (TTY only)
• Bulleted lists (TTY only)

New features

• Structlog output (Implement (optional) structured logging #10)

Addendum

Having reviewing the logging code it actually doesn't look too bad. I'd be tempted to:

• Refactor LBullets into LogList and LogMapping
• Separate out logic for rendering to tty vs non-tty.
• Go through the code and refactor/document anything non-obvious