This commit contains two variations of conversion. The most appropriate
one should be used in a refactored PR.

decaffeinate:
https://github.com/decaffeinate/decaffeinate

- pros
  - retains comments
  - uses es6
    - let and const
    - template strings
  - lists recommendations for further conversion improvements
  - uses one declaration per line (personal preference)
- cons
  - compact object literals on one line (personal preference)
    - e.g. current = {version, support, usage: 0};
  - ifs on one line (personal preference)
    - e.g. if (nums == null) { nums = {}; }

js2coffee:
https://github.com/js2coffee/js2coffee

- pros
  - TODO
- cons
  - TODO

js-beautify -r --indent-size 2 INPUT-FILE

bin.js now requires caniuse-cli.js, and not the coffee-script files.

The new caniuse-cli.js file is a CLI-only file that requires
caniuser.decaffeinate.js

caniuse.decaffeinate.js now provides two main functions:
- toStreams() which will output to either default stdout and stderr,
  or two streams of your choice.
- asString() which will return the output as a string.

This separation will make it simple for other JS code to use the module
to extract the output and use it in other situations, e.g. converting
to HTML.

So we can use the args parser (and more importantly, the default
argument values it provides) in other code, e.g.:

```js
const caniuse = require("caniuse-cmd");

const args = process.argv.slice(2);

console.log(caniuse.asString(args));
```