Send environment variables

[zachgoldstein]

We don't seem to pass any environment variables along with the payload. It should get passed into the Airbrake.log() func, but I don't see that happening. We set the environment (as in prod/staging/etc), inside the payload's context field, but not the top-level "environment" field, which is for env vars.

We can get this via os.environ and set it automatically. I think there should be a field enabling this, but defaulting to be disabled. The env could hold sensitive stuff and we don't want to send that by default.

[kyrylo]

In theory we should implement filters and then users will be able to pass those via them.

[zachgoldstein]

Filters: #48

[zachgoldstein]

@kyrylo My understanding is that filters act to remove sensitive data, where this could possibly add sensitive data to the context? I'm not sure how we would be sending data via filters?

[zachgoldstein]

@kyrylo #52 contains tests that make sure that blacklisted keys do not get sent in the environment payload.

[kyrylo]

I guess you meant #67. Thanks!