Initial top-level doc for structured_facts.md
Edit arm-0 for greater clarity.

- remove passive voice in a few places
- make process for requesting a new ARM more explicit
- rework links to markdown style references
Add required quotes on the index link targets

This is not in Gruber's spec but is apparently required for GFM.
Merge pull request #8 from ahpook/master

Update ARM-0 for clarity; Add content to ARM-5