Initial version of RSpec document

I've created an initial version of the RSpec document.
The compiled version of this pull request can be found at https://fed4fire-testbeds.ilabt.iminds.be/asciidoc/new_rspec.html

This document attempts to describe the geni version 3 RSpec as they are currently in used.


I haven't found a detailed resource on this, so this for the most part a new document. So please report any errors or inaccuracies!
Any comments or feedback?


Note: This part of the document only attempt to describe things as they are in geni version 3 RSpec. 
In the future, we might also describe more RSpec extensions in this document (including new ones).
Changing anything in the core geni version 3 RSpec, would probably mean defining a new RSpec version, described separately.