Usecase: Datatypes in hive are not highlighted without this fix

We can't check for nextChange until all marks have been looked at

See https://discuss.codemirror.net/t/marktext-endstyle-appearing-multiple-times/568/5

Closes #3709

zt was placing 40% of the line above the visible area, and zb was placing it too high.

Issue #3722

Issue #3723

Example: `[foo\[bar\]foo]: https://example.com`

To avoid IE8 parser issue.

Issue #3636
Issue #3698

Closes #3689

Closes #3703

It took me forever to figure out why vim mode wasn't working, and all because the manual said to set the "keymap" option and not the "keyMap" option. I also added quotes to make it clear that "vim" is a string.

There was a typo in one of the comments (`actuall` vs `actual`).

Issue #3708

So that tiny mouse motions don't keep resetting the selected item

Closes #3698

Currently operators in most themes look like normal text because
cm-operator doesn't usually get special styling. This patch highlights
word operators (in/and/or/not) to make them stand out better.

Makes sure the selection is not entirely cleared, which causs the
on-screen keyboard to get hidden.

Disabled for Firefox, where this causes other problems.

Issue #3653

Closes gh-3687

for our purposes (=>|<=|...) works just as well as ((<=)|(=>)|...)

... taking the same approach as the C-like page.

Also
- Changes the window title from Oz mode => MscGen mode
- Makes the samples a little more uniform