Move the testsuite schema out of the jsonschema_suite script

[dolmen]

The JSON Schema for the the tests is currently embedded in the jsonschema_suite script. This forbids any reuse.

Could you extract the schema in an independent file and put it at the root of the repo?

[Julian]

I forgot why I did this. But yeah it certainly sounds reasonable. Any chance you wouldn't mind a PR? If not, it's going to take me a bit to circle back around.

[dolmen]

If I do a PR, I will be credited in the commit as the original creator of the JSON schema file. Which I'm not.

If you do the easy first step (take the JSON shema and commit it in a plain file in the root dir: this is just copy/pasting), I'll take the time to do the second part as a PR (use the separate file from the Python script).

[seagreen]

Close me!