convert plain text docs to markdown

This initial commit attempts to match the formatting of the PDF version
as closely as possible.  There may be some additional formatting needed
or perhaps headings added to make up for the lost of color highlighting,
but those are not included here.
misc changes to API docs

- add "Expected Changes" heading and move after paragraph describing
  that the API is JSON+HTTP.
- change 'URL' to 'API Call' on info endpoint for consistency
- remove leading slash on getStatusCode endpoint URL for consistency
- add intra-page links to objects where appropriate
- fix a couple of small typos