Issue #3039

Since the mouseover will necessarily happen at the very edge of the node, and thus
give ambiguous coordinates.

Closes #2821

This might break sites that depend on async linters getting an editor instance
as first arg, or sync linters getting the .options property of the options passed
as second argument. The args passed are now more or less consistent.

Issue #2681

Bumping them for every release just adds too much git
noise and history blowup.

Closes #2376

Added a wrapper for js-yaml.js to enable YAML lint support. Followed
json-lint.js pattern. Unfortunately js-yaml.js only shows one error at
a time, but something is better nothing. Checked code with linter and
ran tests. All came back clean.

Passing options causes issues in jshint since lint options are also
passed. These options cause bad option errors in the annotation list.

e.g. errors on css `input.someLongClassName {}`

Original error & warning icons had jagged edges due to being GIFs
This made them look quite poor/low quality on dark BG'd themes
So, new, better looking icons added which have been run thru TinyPNG for
compression
Result is fewer bytes than original and they look good on dark BG's too

Issue #1782

Rather than polluting the top-level of the editor object

Apparently Bootstrap messes with those.

Closes #1497

- Link to external jsonlint.js (don't want dependencies in repo if
  I can help it)

- Use a single demo file (prevent demo/ from becoming a huge mess)

- Make whitespace and newlines conform to other files, fix linter errors