Fixes #37

• Replace abandoned dependency semver-compare with semver
  • semver@5.7.1 is last version without nodejs version restriction
• Support any version spec, not just single simple >=X.
• Add generic message when the problem is not simply being below min version (for example: user is on 13 while engines.node is ^12 || >=14).
• Offloads all string-parsing from this module, making it simpler and more maintainable.