Batch scale and resize

Update formation for multiple process types at once from a single command, including both quantity and size (horizontal + vertical scale).

```
➜  ./hk help scale
Usage: hk scale <type>=[<qty>]:[<size>]...

Scale changes the quantity of dynos (horizontal scale) and the
dyno size (vertical scale) for each process type.

Example:

	$ hk scale web=2 worker=5

	$ hk scale web=2:1X worker=5:2X

	$ hk scale web=2X worker=:1X
```