Function between

between(
    source: string,
    start: string,
    end?: string,
    lastEndMatch?: boolean,
): undefined | string
Returns source text that is between start and end match strings. Returns undefined if start/end is not found.
```
// Yields ` orange `;
between(`apple orange melon`, `apple`, `melon`);
```
Parameters
- source: string
  Source text
- start: string
  Start match
- Optionalend: string
  If undefined, the start string will be looked for
- lastEndMatch: boolean = true
  If true, looks for the last match of end (default). If false, looks for the first match.
Returns undefined | string