Let your JS API users either give you a callback or receive a promise.
## Usage
```javascript
var maybe = require("call-me-maybe")
module.exports = function asyncFunc (cb) {
return maybe(cb, new Promise(function(resolve, reject) {
// ...
}))
}
```
## API
### maybe(cb, promise)
If the callback `cb` is truthy, returns `undefined` and will call `cb` when `promise` is settled. The parameters passed to `cb` are standard error-first:
- If `promise` is fulfilled, then it is called with the result of the promise: `cb(null, result)`
- If `promise` is rejected, then it is called with the rejection error: `cb(err)`
