Implemented quiet for the get operation
Merge pull request #8 from lcosmin/feature-get-quiet

New "quiet" option for get operation
libcouchbase.c wasn't updated in the last commit
Add extended mode for gets

When the `extended` argument is supplied, `get` will not
only return the value, but also the flags and CAS value.

    value, flags, cas = cb.get('key', extended=True)

    cb.get(['foo', 'bar'], extended=True)
    # {'foo': (val1, flags1, cas1), 'bar': (val2, flags2, cas2)}
Make extended `get` results a named tuple