Remove hydro

- Not longer using Hydro (to avoid circular dependencies)
- Added test coverage with Istanbul: `npm run coverage`

```
=============================== Coverage summary ===============================
Statements   : 96.51% ( 83/86 )
Branches     : 90.38% ( 47/52 )
Functions    : 100% ( 10/10 )
Lines        : 97.5% ( 78/80 )
================================================================================
```