[ENHANCEMENT] rewrite cli

[lukekarrys]

The CLI is useful for things it can do, but lacks feature parity with the rest of the API. As part of the next major release, the CLI should be rewritten to allow for as many methods as possible to be called via the CLI.

• piping Allow piping into semver to read versions #161

[ljharb]

Please do try to preserve the interface of npx semver $v to normalize/validate a version number :-)