pixi-projection plugin externs

[hypersurge]

I'm attempting to create externs for pixi-projection plugin, and would intend to have them within pixi.plugins.projection. But I'm struggling with understanding the best way to resolve extra methods attached to core classes. For example "pixi.core.display.Container" will receive method "convertTo2d()" when the plugin is used. Suggestions welcomed with thanks.

[ivanpopelyshev]

I dont know how to do it in haxe. Mixins should be possible, right?

I even found a way to do them in typescript with usage of ES6 modules

[hypersurge]

A bit out of my comfort zone ... I'm not aware of a non-macro way for Haxe to handle mixins or dual inheritance? So I've made some compromises and made a start.

https://github.com/hypersurge/pixi-haxe/tree/dev/src/pixi/plugins/projection

If I get things stable I'll make a PR back to here. Thanks @ivanpopelyshev for the Projection plugin.