Static typings, underscore properties & security vulnerabilities

[DonovanDMC]

This:

• makes typings static, as generated types are usually either lacking information or are less than helpful
• adds underscore properties via defineProperty, to make the non-enumerable
• updates jsdoc-to-markdown from 6.0.1 to 7.1.1 (I saw no changes in the generated docs)

I've left any methods/properties that begin with underscores out of the types, assuming they're "private"/"internal" methods and shouldn't be used
This ties in with jirenius/modapp-eventbus#1, the comment on line 23 can be removed if that goes through