Document all supported `spec.json` properties

[chrispcampbell]

The spec.json file is still being used by lower-level sde CLI tool commands like sde generate (and will likely continue to be used for the foreseeable future), but we don't have a single place where all the supported properties are defined. We should add JSDoc-style documentation/types to the compile package since the parsed spec object is a parameter to the top-level parseAndGenerate function exported by the compile package.

I'm adding this to the 1.0 milestone because this is important to document before we declare 1.0 versions of the related packages (cli and compile).

[ToddFincannonEI]

I added some of the more recent specialized properties in the spec.json file. I could write up descriptions for those if it would be helpful.