Updated packages.
Improvements to tooltip handling.
Fix (hack) a small timing bug.
Respond to keypress sooner, to reduce visible lag.

(Syntax highlighting was quite laggy when typing).
Register Dart language.

Allows setting of tab sizes, etc.
Handle indenting better.

This isn't ideal; closing brace won't automatically un-indent, but we
might be better calling Format on the block when a closing brace is
typed?