Diagnostics error occurs when an @ is used in the file path

If the path of a file has an `@` in it, an error will occur with diagnostics.

For example, I have a folder called `@Projects`. This causes the error to occur in VSCode when I save.

`Invalid format: Projects/FlixelTut/source/PlayState.hx`

The issue appears to be a compiler bug, probably a string.split() that goes wrong. Based on discussions with @Gama11 in Discord, we believe that Haxe does a a naive string split on @, assuming that can't appear in file paths.