Reorganize tests to be one file per module and to give more descriptive file names

[CFiggers]

Historically, spork's tests have been organized into numbered suites, such as suite0002.janet. Each suite usually contains tests related to a single module. But some suites mix together tests for unrelated modules (without an apparent intention to doing so).

More recent additions and updates in the spork/test directory have switched to using an (IMHO) much friendlier convention. These newer test files simply name the test file after the module it is primarily focused on testing, prefixed with suite-. This makes test cases for a given module much easier to find. Discoverability of test cases matters because in many cases the tests are the only documentation or usage examples available for a given spork module.

This PR proposes renaming and lightly reorganizing spork's tests to entirely switch over to the more recently-preferred convention. The goal is to improve the discoverability and therefore usefulness of test suites as quasi-documentation. The tests themselves are unmodified and all still pass.

[sogaiu]

I tried your branch and tallied the number of tests before and after and the counts seem to match.

LGTM :)