New rule: package.json validation for NodeJS

[iamwillbar]

• [ ] license parseable as a SPDX expression
• [ ] description provided
• [ ] keywords provided
• [ ] homepage provided
• [ ] author provided
• [ ] main provided
• [ ] repository provided
• [ ] test script provided (and isn't the default error script)

[hyandell]

I was pondering whether it would be nice to implement this by having an axiom for 'build system' or 'package manager'. Then you could do:

package-manager=npm -> add the above rules using existing rule language

[hyandell]

packager axiom implemented. Need to PR.

[hyandell]

See #105