definition of ProcState in Chapter 15

It's mildly confusing, but in the book, starting from section 15.2.3, the following definition is given:
```
data ProcState = NoRequest | Sent | Complete
```
whereas in this repo, `ProcessIFace.idr`, `ProcessLib.idr`, `ProcessState.idr` define it as
```
data ProcState = Ready | Sent | Looping
```