Added context manager for Device ('with'-support)

[RobertoRoos]

I added __enter__ and __exit__ methods to enable context manager support. This makes uses of a device more pythonic.

I also renamed device to Device, since it's a class. I added an alias with a warning for device, so existing code would keep running.

Having said this out loud, the class renaming should have been a separate PR. Let me know and I'll split it again.

[RobertoRoos]

Usage is now:

h = hid.Device()
with h.open(...):
    # pass

I would prefer:

with hid.open(...) as h:
    # pass

Much like opening a file.
Something like this could be more easily implemented with #109 .

[prusnak]

Can you please add backwards compatibility for the rename, so also the old device would still work the same way? Maybe just device = Device would suffice.

[RobertoRoos]

@prusnak I've added exactly that.
device extends Device with a warning in the constructor.

[jonasmalacofilho]

Hi,

I'm sorry for the unsolicited review, but as the maintainer of project that depends on cython-hidapi, I reviewed this and also tested it for backwards compatibility.

I left a few comments, please take a look at them when possible.

[RobertoRoos]

Reverted all (potentially) breaking changes.