Moved some floating tests into haas/_tests.

This is a convention we've been following on other branches.
Slight readability enhancement in the README.

The long url in the middle of the text made this a bit awkward to read
(and it didn't really fit within the line-length the document is
shooting for). The footnote style links are better for this.

I'm going to add some links to testing documentation, wanted to clean
this up first.
Wrote some documentation re: testing procedures.

This included adding a test-requirements.txt, to make the documentation
accurate. I also adjusted the pointers to documentation in README.md.
Deleted some stale/unneeded files.

It's been so long since anyone's used these that I don't even
remember why they're here.
Merge branch 'unit-tests' into newapi

Conflicts:
	README.md

I also deleted the model tests that were on the unit-tests branch;
they're all written with the old api in mind, and would be tricky to
port, without much gain.

Some of the other tests are failing, which is hardly a surprise; the
restructuring of haas.model has surely broken many things.