This fixes various issues such as:
- missing space in Dart version between the live demo and demo source
links.
- Live example link directing to Plunker for Dart.
The main mixins (`liveExampleLink`*) used to support the generation of
links now assume reasonable default values for their arguments, and in
most cases the defaults are used.
* Dart example links: use http vs https
As agree to with @kwalrath.
Mainly copyedits, but also
- Dart .jade extends TS .jade file with minor overrides
- Significant update of example code (so it matches the ts example in its
appearance and behavior).
- Tweaks to Dart code.
- A few extra/corrected mixin definitions in `_util-fns.jade`.
Patrice Chalin
Foxandxss
Naomi Black
Ken Dale
Aristeidis Bampakos
Ward Bell
joeeames
Filipe Silva
Josh Otis
Peter Bacon Darwin