get rid of the extra, project-specific (python) package

in practice we found it hard to keep project-specific things in a separate package and leave `restbase` mostly untouched.  also, the location of existing code and the question where to put new code causes confusion rather quickly.

the new policy is to only use one package, which we will extend and modify to meet a project's needs.  in order to make it easier to merge things back and forth, we'll keep the module name generic, though.
don't use "foobar" for anything that's not the project/package name

this way all occurences of "foobar" can simply be replaced with the project name when starting a new one...
explain what this is for at all...
we can use relative imports instead of import hackery...
(almost) avoid using the name "restbase" in code

also try to not import anything from the module outside of actual tests (or fixtures)
we want tests to be included in the coverage report to see if we're running all of them...
with "pytest" the `tests/` directory needn't and shouldn't be a python module
also encourage relative imports in the doc examples
use insanely clever name to hint at the new policy of having no extra, project-specific package

dropping the "base" part should reflect that the package is not the base package for a particular project, but the project package itself.  instead we add "back" to make it clear this is the backend...

also see b36e2da3 for more details
Merge pull request #2 from pyfidelity/simplify-package-structure

simplify package structure