---no-install also when the package exists

[natlibfi-arlehiko]

The description for the flag --no-install says: Skip installation if a package is missing.

How about skipping installation even if the package exists (And maybe bind that behaviour to another flag)? When you run npx <some-package> the NPM registry will always be queried for a newer release. When you repeatedly execute CLI commands you don't want to do that.

It'd be much nicer to say: npx --no-install <some-package> than node_modules/.bin/<some-package> or even $HOME/.node_modules/.bin/<some-package> (You can run npx anywhere, regardless if there's node_modules in your cwd or not).

Also see #214