Remaining tasks for full publication of the "is" functions

[gwhitney]

• [ ] Declare Range and ResultSet types in types/index.d.ts and make the associated "is" functions into guards; also add type tests for them into types/index.ts
• [ ] Provide website documentation for the "is" functions for which it is missing.
• [ ] Make all of the exported "is" functions available in the Parser
• [ ] Make sure embedded docs are available for all "is" functions.