Require a main class, even for .swc.

The Haxe compiler seems to require either a main class (-main) or entry
class (no -main, just class name) when compiling swc/swf. The latter
doesn't seem to work well with dead code elimination and would
complicate a bunch of things, so just require the main.

@connec, what do you think?
Process all unhidden .hx files in the current directory.
Haxe 3 property syntax.