Start moving issues into tracking document, minor docs example tweak

[mikemee]

Note: This PR only affects document files. It does NOT change any code.

To try and help out (after checking with @stephencelis), I've been going through the issues to pull out enhancement requests and also to propose a roadmap for priorities. This PR is my first stab at this. If accepted, I'll close the referenced issues.

Why? My thesis is that the less open issues the better, for the following reasons:

• many projects have a roadmap and this can be a useful guide for people and cut down on repeat questions
• it's nice to see if a feature request has already been made and find a link to the history (via a closed issue, in this case)
• if there are just a few issues open, it's easier to look for things to help, or known problems
• I often judge a project's quality by how many issues are open and how long they've been there. Not a great guide, but I'm sure I'm not alone.

[mikemee]

@stephencelis If you're in a PR merging mood, it would be really helpful to do this one too. It's completely orthogonal to other pending PRs - just a doc change, and will let me close 4-5 issues. Thanks!

[stephencelis]

Looks good to me!