Proxy support

[themylogin]

As aiohttp won't support setting up proxy from environment variables (aio-libs/aiohttp#529), I've had to implement it as a transport option.

Example usage:

sentry_dsn = "https://public_key:private_key@sentry.io/1234?proxy=http%3A%2F%2Fproxy%3A3128"

[asvetlov]

See also aio-libs/aiohttp#2256 -- it introduces proxy_from_env() function.

[ashwoods]

And afaik Sentry deprecated options on the DSN, at least for the transport, in favor of explicit class loading: getsentry/raven-python#587

[azhurbilo]

What the status of this Proxy feature?
May be others know any workaround?

It's impossible to use this client when application access to public internet blocked by firewall :(