new SjlMap(iterable)
`SjlMap` constructor. Has same api as es6 `Map` constructor with
an additional couple of convenience methods (`addFromArray`, `addFromObject`, `iterator`, `toJson`).
Parameters:
| Name | Type | Description |
|---|---|---|
iterable |
Array | Object | The object to populate itself from (either an `Array<[key, value]>` or an `Object`). |