Improve httpie output

[ulope]

It would be great if the httpie output were to be a bit more 'idomatic'.
I.e. instead of piping json or raw data into the command and manually setting Accept and Content-Type headers use the built-in support of specifying values (JSON or GET / form) directly as arguments.

[datakurre]

@ulope Could you provide some examples? I'm not really familiar with httpie myself.

The best would be, if you could provide preferred version of the http/httpie commands found here https://github.com/collective/sphinxcontrib-httpexample/blob/master/tests/snapshots/snap_test_builders.py