fix bad sorting of negative dates

[seanlowe]

v2.1.13

Fix issue: Timelines with negative dates render in the wrong order #22, and some other miscellaneous changes.

Changes:

• write new function for sorting the unique timeline date ID's
• overhaul function buildTimelineDates to accurately handle use cases where the built-in JS Date object fell short
• write new function cleanDate to take a normalized date and return one where all leading zeros have been removed
• changed normalizeDate to append a 01 instead of 00 for missing hour sections
• small docs change
• added a contributors section on the README
• updated LICENSE to 2024
• deleted unnecessary copy of README from before docs overhaul

---

Resolves #22