[Feature Request] Support for Remapping Packages #248

I was working on openfl/openfl-js#11, but realized that, if a library exports itself under 2 namespaces like that, users will stumble upon issues REALLY quickly.
One example of this is, say the library exports itself as openfl.* and flash., but another library depends on it compiles using the openfl. version of classes, this will immediately cause issues to the end user if they want to use the flash.* version, because e.g. flash.display.Bitmap isn't the same as openfl.display.Bitmap to the compiler.
I believe for this reason, there should be a feature similar to Haxe's --remap compiler flag, that allows a package to be imported under another name, for compatibility reasons.