Issue papers ported to GitHub from the wiki

I have ported the COGA issue papers from the wiki:

https://www.w3.org/WAI/PF/cognitive-a11y-tf/wiki/Gap_Analysis_Issue_Papers

to the GitHub repository:

https://w3c.github.io/coga/issue-papers/

Please make edits now in the GitHub repository, not the wiki.

For the porting pass, I made only minimal editorial changes. There are a 
lot of editorial issues we need to fix before advancing these. A raw 
list of starter issues:

  * There should be no naked URIs - links should have human-oriented
    link text, not the URI as the link text.
  * The papers should probably have a consistent organization with each
    other.
  * Citations need to be made inline.
  * There should never be a single sub-section - either there are two or
    more, or there is no need for a subsection. Same for list items.
  * Watch for homonyms (e.g., affect/effect).
  * Remember W3C uses U.S. English. Some terms and spellings need adjusting.

Probably we need to set up a style guide for the COGA group, both to 
describe the structure chosen for issue papers, techniques, etc., and to 
address particular things like what I saw while porting this stuff.

Michael