Switch test config files from INI to JSON format?

[waylan]

As pointed out in #332, the testing frameworks' config files use the INI format, which is rather limiting. Perhaps we should switch to JSON - which being essentially the same format as Python lists and dicts, makes it very easy to represent pretty much any key/value pairs to pass in to extensions. This might eliminate the need to the tests/test_extensions.py file.

Note, this was not done originally because, at the time, we supported older versions of Python which did not have built-in support for JSON. Currently, our lowest supported version of Python is 2.6 -- the version in which the json lib was added to the standard library.

I also considered using just pure python files, but then they would need to be imported, and as they are in dirs with a bunch of test files (not python modules - no __ini__.py files), that could get complex. While doable, I think JSON is probably an easier lib to work with and more likely to be familiar to future maintainers than importing python files not available on the Python path.

[waylan]

For the record, I used YAML rather than JSON. JSON is a subset of YAML, so if you wanted to use JSON in the config files it would still work. However, I find YAML (without JSON's curly brackets) much easier to read and write. While YAML is not in the Python Standard Library, it is so much easier today to install deps and we already are installing many deps for tests to run. As it is all automated (with Travis and tox), it is not a big deal IMO.