Add support for the Dart language.

[shamblett]

I wish to update NClass to also support Googles Dart language with the addition of class diagrams for Dart and code generation for Dart.

To that end I have forked the repo here where the changes I've added can be found on the 'dart' branch.

As of now I have added support for class diagrams specialized for the Dart language in a similar manner to those for C# and Java. the next step is to look at code generation.

I'll update this issue as I progress

[gbaychev]

Well, that's great! Thank you for your job! Just drop me a PR, when you're done.

[shamblett]

OK, I've created #61 for the initial merge of Dart language support for for NClass.

This covers Dart class diagrams and code generation.

There is a little more to do for Dart code generation to tidy up some language details but there is more than enough done to warrant a PR now, this update is large enough as it is, future work can be done on other issues.

I've added some test projects for Dart in src\Tests\DiagramFiles\Dart which represents the testing I have done thus far.

I've installed the generated msi package, this seems to work OK.

Anything else you need please ping me.