Feature Request: Recursive Directory Searching for function.json

This is currently on the nodejs and the python function roadmap and I'd love to see it here. I have clients that need this funcitonality. To be specific:

This works:

```
app/
├─ SomeFunction
│ ├─ function.json
│ ├─ run.ps1
├─ Other Function
│ ├─ function.json
│ ├─ run.ps1
```

I think this should:

```
app/
│ ├─ functions
│ ├─ SomeFunction
│ │ ├─ function.json
│ │ ├─ run.ps1
│ ├─ Other Function
│ │ ├─ function.json
│ │ ├─ run.ps1
```

I'd be happy for a special subfolder called functions/ if that is easier or to be able to configure the root of your function would work too, but recursive search I think would be best.