Reducing the size of build matrix.

Having a large build matrix causes long building time. It is because Travis runs at most 5 builds at a time for each repo.

This is an attempt to reduce the size of our build matrix by:
 * Running the sys tests in their corresponding target build.
 * Merged "misc" into "macro" build.
 * For each 3rd party lib, run its tests in the related target builds. e.g. openfl-samples is run in cpp build.

One problem is that Flixel's command line tool requires loading lime.ndll. That means testing Flixel requires rebuilding the hxcpp/OpenFL stuff even in the flash/js builds...

I'm not fully satisfied yet, but at least this is an improvement. 
If you're fine with it, you may merge now. I will keep trying to improve it.