Closes #3504

(not *totally* confident about its correctness, but it looks like a
plausible fix, and seems to work ok)

Closes #3500

I don't know if

1) there's a way to get haxe to, while in functiondef, for instance,
   be able to tell the compiler that what it thought was a type name
   is actually a variable name, and to indent/highlight correctly

or

2) there's a way that, assuming it's a type name, to still indent
   correctly

but it is possible to loosen the lexer to accept things marked as
types as function names (in functiondef), and this fixes the
indentation problem.

Node's 'mime' package gives me text/coffeescript for this.

Closes #3343

Closes #3498

Closes #2962

Closes #3245

Issue #3257

Closes #3386

Issue #3431

Issue #3431

Issue #3431

Closes #3458

Issue #2101

Closes #3494

Closes #3492

Issue #3488

Issue #3487

Issue #3462

Closes #3475

Closes #3476

Issue #3474

Closes #3470

More than once people have asked questions expecting markdown mode to
support GFisms and were simply not aware of gfm mode existance.
Hopefully this will make it more discoverable.

Fixes #3449

And remove some unused state properties