completed the Makefile to detect and run `npm install` when necessary for the success of the build process.

Also added the Makefile targets 'clean' and 'superclean' (naming and intent mimicking these targets for any GNU autotools project: 'superclean' blows away the entire npm install set and thus ensures the next `make` build will create a completely fresh output.
ignore all minified files: those are output of the Makefile build process