Consider parse function for str to bool

http://stackoverflow.com/questions/715417/converting-from-a-string-to-boolean-in-python

Probably something like this is best, as it's strict but reasonable:

```
def parse_bool(val):
  if val in [True, 1, "True", "true"]:
    return True
  elif val in [False, 0, "False", "false"]:
    return False
  else:
    raise ValueError("Not parsable as a boolean: %r" % val)
```
