Also update the mode loading demo to make use of the info in that
file, allowing filenames and mimes to be entered.

Issue #2828

Closes #2623

Issue #2529

Issue #2494

It has been superceded by keymap/sublime.js.

The header classes for specific levels of headers, which should set the size of each header did not match the classes in the editor. This commit fixes that.

And fix example code in demo.

Issue #778