improved internal structure for tests files

[daltonserey]

TST should be able to read tests from json/yaml files with one of two different structures: 1) an array of tests; and 2) an object containing a "tests" property mapped to an array of tests. An array of tests is an array containing objects with input and output properties. Json/yaml without an array of tests should be silently ignored. Json/yaml containing incomplete tests should make tst fail.