make.sh: add conditional include operator ('+') and extend platform include/exclude scheme to MODULES and PLUGINS.

For example, you can now do something along the following in MODULES:

config eventloop ln_core ln_glgui rtaudio!android usbrtaudio+android

This allows compilation of select/different modules on particular platforms.

The '+' and '!' operators can be used in LIBRARIES, MODULES and PLUGINS.