Add documentation for storage.Blob's special methods (contains, next, etc)

[jgeewax]

Right now it's not really clear how to check for a key's existence (do I need to do if Key('name') in bucket? or just 'name' in bucket?

We need to make sure these special methods are documented with examples in the API docs for the Key class.

[tseaver]

The implementation of bucket.__contains__ "wants" a string, but is actually willing to take a string and convert to a key. I would be in favor of dropping that myself, and asking the user to create the key, either via bucket.new_key(name) or by instantiating Key directly.

[jgeewax]

I think it'd be annoying to need to create the key to check for existence -- I kind of like the magical "we know what to do if you pass us a string".

So:

print 'my-key-name' in bucket
print Key('my-key-name') in bucket
print bucket.new_key('my-key-name') in bucket

should all return a boolean IMO.

[tseaver]

You're in luck then: we already DTRT.