Ready version 1.0.0

Extend `HTTPService` from [requests.Session](https://requests.readthedocs.org/en/latest/api/#request-sessions).

A new pull request born from [this one](https://github.com/yola/demands/pull/9)

One of the last pieces of feedback given:

> Maybe we should order keywords in the same way as in `requests`?

As I was digging into `requests` I noticed A LOT of code in `demands` was duplicating what is already written.  This is bad.

By extending from `Session`, No longer need to implement our own get/post/put/patch/delete/options methods nor our own Request object.

Demands is now more simple: it overrides the request method to *demand* a successful response.

Other features: makes it easier to set username/password and User-Agent.  Note, I have no idea if these features are used or needed but are present in the rewrite to maintain old functionality.