fix: use noop logger by default

[iskorotkov]

Changes:

• added interface Logger
• added global variable logger
• added method to change global logger
• replaced all log package references with logger global variable
• use noop logger by default

Reasoning:

• correct me if I'm wrong, current implementation prints debug data every time certain function is run. This simple PR disables all logging by default, but library users can supply their own logger and turn logging back on.

The solution isn't very flexible or configurable as I tried to keep it as simple as possible.