json0+text0+rich text OT port to Dart lang

[Dmitry]

I've been keen about Dart lang lately and plan my ongoing project to be written in it. Thus I had to rewrite my recent OT stuff to Dart, including json0 type I need to make everything work. So if anyone out there working with Dart too and want bring some OT stuff, you might want to check this out:

https://github.com/dmitryuv/otdartlib/

ported ottypes:

https://github.com/dmitryuv/otdartlib/tree/master/lib/src/ottypes

This will completely replace my previous work on rich text OT I posted earlier in this group, and going forward I'll work only on Dart version.