Updated `sx-request-make` to use a consistent format for both `POST` and `GET` methods

  (sx-request-make): Added optional arguments for using "POST" and AUTH
  when performing requests
  (sx-request--build-keyword-arguments): Add option of using AUTH and
  including in query when required.
  (sx-request-build): Removed
  (sx-request--request): New function to perform query with all
  variables let bound.

  sx-auth.el: Updated `sx-auth-root` to be full auth URL rather than
  lack method.
  (sx-auth-authenticate): Remove dependency on `sx-request-build` and
  perform construction inline.
I'm not sure what the current authentication logic is, but wouldn't it be better to automatically use authentication if the key exists?
Then the third argument could be changed to something like `needs-auth`, and we throw an error if `needs-auth` is non-nil but no key exists.