schema: support multiple positions at a single company

[waynr]

I am currently migrating from my own bespoke resume data format to jsonresume and have run into a blocker in the sense that my current resume typesetting document can display more than one title and a start/end date range for that title for each work section. I feel this is important to show the trajectory of promotions through one's career (if desired).

This proposed solution maintains backwards compatibility with what was in place before by simply adding a new pluralized "positions" section and leaving the old "position" section as-is.

[teddybradford]

👍 I think it would also be nice to include summary and highlights fields per position.

[waynr]

@teddybradford I'm happy to add that, but I personally won't use it in my resume generator. Are you planning to use those fields yourself?

[waynr]

I'm actually going to wait for the maintainers to review this before changing anything.

[teddybradford]

Sounds good! I follow the format pictured below for multiple roles at a single company, so adding in at least highlights is necessary for me.