raise error when error value from lib is non-zero

[brentp]

closes #36

[Araq]

Well the open returns a bool, why would it raise an exception? This seems to be a breaking change.

[brentp]

I don't disagree. That's why I asked in #36. What do you suggest?

[Araq]

Return false for an error?

[brentp]

that's the current behavior, but there's no to get the cause of the failure.

[Araq]

Hmm, I dunno. Introduce another constructor then that returns an Error type, maybe. Not everybody cares why open failed, if it failed, that's often all you need to know.