README, schema guide, and licenses

[mhpob]

Accidentally committed to the wrong branch, so this is a little overzealous with a "renaming" of the repo in the README. This PR:

• Updated the README to a new name: "latitudes", a forced acronym for "Library of Aquatic Tracking and Telemetry Data Samples". This can change, but I figured this project is now deserving of a neater name than "demo-data".
• Added a permissive CC-BY-4.0 license for the general library. I'm not committed to this and don't really know anything about licensing -- it was just a stab and can change in the future.
• Added a licenses/ directory to house the licenses of individual files
• Added a guide to the current yaml schema. IMO this should in no way be considered final! Just a start.
• Added a requirement that data submitters provide a license for the use of their data here and elsewhere
• Added a requirement to note the vendor in the transmitter summary in the metadata