Avalonia support

Avalonia

TODO

• create a branch for Avalonia stuff (and we will then proceed to work on that branch using PRs with the usual branching policy, almost as with the master): feature/17-avalonia
• make PR #98 non-destructive (because currently it destroys stuff, and that’s unwanted) and merge it into the branch
• fix builds and add CI support for both modes (WPF and Avalonia)
• rebase work of @ahopper from #170 on top of the branch
• make sure tests work for WPF part
• make FormulaBlock public
• solve #63 in the branch
• remove the code duplication (at least most of it) — that’s why #63 was necessary
• update the documentation
• after all of that, Avalonia may land into the master branch
• add packaging for Avalonia, but explicitly mark the packages as alpha (#192)
• check issue #128: it should’nt be reproducible for WPF and for Avalonia
• currently we’re planning to only allow for solid colors in the portable code base; we’ll have to think about supporting for non-solid colors (aka Brushes) for WPF- and Avalonia-dependent code
• Make sure the resources (.xml and .ttf) are deduplicated properly.

[ForNeVeR]

Hello, @Happypig375!

Your request totally makes sense. Could you please raise another issue about Xamarin Forms? I’d like to support it, although I’ve no knowledge of Xamarin at all. I’d consider this request as up-for-grabs at the moment.

[ForNeVeR]

Thank you so much, everyone. We did it!

The next release will likely have full Avalonia support.