Allow anonymous event logs

Currently log interface requires an event name followed by optional context object, e.g.:
```
logger.trace('compile', {foo: 'bar'})
```
Idea is to allow an alternative signature where just the context is passed, e.g.:
```
logger.trace({foo: 'bar'})
```
In pretty mode could just have the event part dropped, e.g.:

With event:
```
– trace a.b.c:foo  --  a: 1  b: 2
```
Without event:
```
– trace a.b.c  --  a: 1  b: 2
```
The event field in anonymous events could be anonymous. Just dropping the key altogether would be better for bandwidth though––how much? Could be a production-time optimization...

Sometimes you want to log something but don't have a strong concept for an event name. Might be especially true for trace level.
So, want the API to scale gracefully from temp/unsure/lightweight logging to more robust/long-term/production logs. Logging should be as fluid/easy as possible to start out. Forcing an event name feels to add too much burden.

prisma-labs / graphql-framework-experiment