quick fix for cleaning and re-creating the package.json file under all circumstances
- Makefile: added targets: superclean and npm-install

- Makefile: complete the .PHONY target set

- make sure 'make' and 'make all' run 'npm install' ('make npm-install') as well: the goal is that this command sequence should succeed and rebuild the library completely afresh: `make superclean && make`