Add Version File Parsing, Make Versions Optional in use, install

[beeequeue]

If a version is not specified for the use and install commands nvm-rust will look for and parse any files containing Node version specifications amd use that!

nvm-rust handles files containing ranges, unlike nvm.

e.g.

// package.json
{
  ...
  "engines": {
    "node": "^14.17"
  }
  ...
}

# Installs 14.19.3 as of the time of writing
$ nvm install