Correct docstring typos

There are small typos in:

    couchbase/cluster.py

    couchbase/search.py

    couchbase_core/mapper.py

    couchbase_core/priv_constants.py

    couchbase_tests/base.py

    docs/source/api/acouchbase.rst

    src/pycbc.h

    txcouchbase/cluster.py

Fixes:

    Should read representation rather than reprentation.

    Should read internal rather than interanl.

    Should read initial rather than inital.

    Should read fails rather than failes.

    Should read identically rather than identially.

    Should read elsewhere rather than elswhere.

    Should read contains rather than constains.

    Should read connection rather than conneciton.