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It has been superceded by keymap/sublime.js.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

Issue #2085

Closes #2080

Add getHelpers and registerGlobalHelper, allow modes to specify arrays
of helper names, support modeProps in mode specifications.

Update foldcode and show-hint to make use of more powerful helper
system by defining an `auto` helper that tries multiple helpers, and
using that as default.

Issue #2025