Refactoring README.

- Moved Canonical Name listing to separate README_NAMES.md file
- Heavy editing of README to remove duplicated information (consolidated into tables, etc.)
- Moved example content to separate sample.json file
- Minor fix to links on validator page

@geordanr @voidstate @fab7431 Please review (note: the README is probably best viewed using the "View" button rather than the diff)
It looks like using `---` only works once, to delineate the header row.