Created api comparison doc with initial pass of auth, users, and posts comparison info.
Reformat to column comparison
Correct link format
Delete meta is available on dotcom

Props @justinshreve for clarifying.
Group meta comparison
Add taxonomies comparison
Add media comparison
Add comments comparison
Add further site comparison docs
Add XML-RPC comparison
Add key
Add post periphery comparison
Add revision comparison
Add custom authentication comparison
Add page comparison
Add post retrieval-by-slug comparison
Add extra text
WP.com's API exposes extra data via /help
Note XML-RPC can only give limited subset of options
Remove empty taxonomy rows