Support for `debug()` under `Printer`?

Currently if I wish to print debug messages, the usage is something like this:

```
from wasabi import msg
msg.info('Hello', show=is_verbose)
```

But now `is_verbose` is scattered everywhere in code. I'd like to propose a class-level variable for `Printer` that sets the `is_verbose` flag once with the `Printer` and a `msg.debug()` function that will print based on this flag. Essentially a flag for log level is what I am looking for.

Proposed Usage:
```
from wasabi import Printer
msg = Printer(is_verbose=True)
msg.debug('Hello') # This prints to console
msg = Printer(is_verbose=False)
msg.debug('Hello') # This does not print to console
```

Let me know if this usage makes sense and I can contribute a PR or maybe there is an existing way to achieve this functionality that I am probably now aware of? :)