send_event method does not return http status

[leandropadua]

Currently the response is not available to the user to make decisions based on the http response code.
For example, the current code will not raise an exception if the API_TOKEN is invalid and will give an impression that it was a successful execution.
The status code is only visible as a debug message (DEBUG: Sending to SignalFx failed (401 Unauthorized)), which is not accessible in code.

with signalfx.SignalFx(ingest_endpoint=SFX_INGESTION_ENDPOINT).ingest(SFX_API_TOKEN) as sfx:
    sfx.send_event(event_type='deployments')

[leandropadua]

I have proposed a solution in this PR #120

Seeing the same with sfx.send() function.

[akaars]

An issue regarding the inability to detect authentication errors was raised in 2016 - #28
Probably it's too complicate to deal with that...