Allow setting a raven.Http request in place of http.Request

[flimzy]

In our application, we want to set the Data fields in the raven.Http struct which is logged.

logrus_sentry currently doesn't make this possible.

I see two possible solutions. The easiest one would be to make getHTTPRequest() return a raven.Http struct, either creating it from a http.Request, or returning it directly if it's already a raven.Http struct.

The more general solution would be #29. And even then, if #29 is decided to be a good idea, there might be room for both.

What do you think?