add scss include_path support

Windows support

Windows support - fixes issue #49

Conflicts:
	Makefile

Improved Makefile

* Remove "-c" from CFLAGS and hard-code it into the recipe -- CFLAGS
  should be overridable from the command-line but not including "-c"
  should never invoke the linker on object files
* Use real target names for library files instead of phony targets
* Add install and install-shared targets
* Use $(OBJECTS) instead of *.o
* Use .PHONY to properly mark phony targets

Conflicts:
	eval_apply.cpp

Don't think we need to eagerly evaluate numeric values after all, now that we're fully evaluating function args.