Add docstrings to pacify pylint.

See https://github.com/GoogleCloudPlatform/gcloud-python/pull/238#issuecomment-58954981.
Typo.

Incorporate feedback from @dhermes.
Avoid 'wrapper' in module docstrings.

Incorporate feedback from @dhermes.
PEP8:  single-line docstrings.

Incorporate feedback from @dhermes.
PEP8:  this time for sure, Rocky
Merge pull request #240 from tseaver/docstrings-datastore

Add gcloud.* and gcloud.datastore.* docstrings to pacify pylint.
Documenting undocumented classes/methods/etc. in gcloud.storage.

Also did tiny clean-up along the way in places I noticed
code issues.

Another thing, I suggest a rename of _bytes_written in
storage.iterator.KeyDataIterator to something like
_bytes_read or _bytes_consumed, i.e. something which
actually matches the action being taken.