add CLI tool for module replacement suggestions

[gradrrs]

• Added CLI tool replacer.js for replacing imports and require calls.
• Added executable bin/replacer.js for running from terminal.
• Updated package.json - added bin section for using CLI tool.
• Added comments and basic structure of CLI applications.

[43081j]

sorry to cause some chaos but we've started building an e18e CLI over here:
https://github.com/e18e/cli/

i think this belongs there rather than here.

i was going to work on it myself, but if you want to help implement this in the e18e cli, we'd be happy to have the contributions

otherwise, ill likely pick it up and add you as a reviewer to ensure it does the same job