CaptchaServerHttpClient should extend the base, not matrix http client.
Refactor the HTTP clients a little.
Oops, I removed this param.
Separate out the matrix http client completely because just about all of its code it now separate from the simple case we need for standard HTTP(S)
Merge branch 'develop' into http_client_refactor
Merge pull request #20 from matrix-org/http_client_refactor

Http client refactor