Take over try.haxe.org by HF

Hey people.

Since http://try.haxe.org/ is currently down (ping @clemos) and there's a new unmerged development of tryhaxe supporting macros by @mrcdk (http://try-haxe.mrcdk.com/), I thought how about we take the project under the HF's wing to provide official support and development for it.

Right now I feel like it looks kind of weak that the thing that seems to be pretty official (e.g. it's under the haxe.org domain) is not really developed and noone from HF is responsible for it being broken. This is a good resource that we should take care of.

I'm not sure if we have the server management resources for that, since @andyli is pretty busy with other stuff, but I think I could help with the further development. For example I was thinking that we could improve the editing experience by integrating this new [Monaco](https://microsoft.github.io/monaco-editor/) editor that powers VSCode and the [Haxe Language Server](https://github.com/vshaxe/haxe-languageserver) so we have fancier completion, hover helps, goto definitions and other stuff.