feat: add GetKeys to get event keys

[julienrbrt]

As far as I know, there is no way to get all the keys of a particular event.
This is handy (even though expensive), to use in hooks.

[julienrbrt]

Gently pinging you @rs, this would greatly help us.

[rs]

This won’t work until event is “closed” (sent) and won’t work with bson encoding. I’m not for adding/maintaining this. Thanks for the suggestion.

[julienrbrt]

This won’t work until event is “closed” (sent) and won’t work with bson encoding. I’m not for adding/maintaining this. Thanks for the suggestion.

This makes sense, thanks for your review! Would you know a solution for reaching the same goal?

[rs]

You can set an io.Writer wrapping your output writer that decodes JSON on each call the Write. It is guaranteed that each write will get a full event.