Project.py - does not accept -b ?

Looks like a regression.  It used to be allowed to use `-b` : 

Currently:

```
python tools\project.py -m K22F -i iar -n MBED_10 -b
usage: project.py [-h] [-m MCU] [-i IDE] [-c] [-p PROGRAM] [-n PROGRAM]
                  [-b BUILD] [-L] [-S] [-E] [--source SOURCE_DIR] [-D MACROS]
project.py: error: argument -b: expected one argument
```

@screamerbg @theotherjimmy @sarahmarshy 
