add some TODOs and add ConfigException to __init__ for convenience
add erosion application config as a holistic test
parallelism name changes: validation -> validators, value_type -> validator (might even change this to converter later, who knows, i'll have to ask mark)
get rid of LayerSet, it wasn't solving anything. environment/layerset selection should happen external to strata, choosing amongst multiple strata configs
flesh out a couple numeric validators
first step in getting rid of old-style requirements
continuing the effort to excise requirements, introduce validation, and keep tests running
rephrasing and refactoring internals of ConfigSpec processing
strip out a bunch of the old sorting logic, which has been superseded by lazy population
add a test for dependency cycles
add an indirect dependency cycle test and improve the dependency cycle message
add a couple notes and a couple base case tests
first pass on the minimum permission checking