Document exceptions (currently) raised from 'Bucket.delete'.

Note that #164 would change this (by adding fine-grained exceptions
for 409, 401, etc.).

Fixes #159 (but should be revisited if #164 lands).
Document exceptions (currently) raised from 'Connection.create_bucket'.

Note that #164 would change this (by adding fine-grained exceptions
for 409, 401, etc.).

Fixes #166 (but should be revisited if #164 lands).
Rename key iterators to indicate they are implementation details of Key.

Rename 'key.KeyIterator' -> 'key._KeyIterator'

Move / rename 'iterator.KeyDataIterator' -> 'key._KeyDataIterator'.

Fixes #244.
Merge pull request #322 from tseaver/166-document_exceptions_for_connection_create_bucket

Fix #166: Document exceptions (currently) raised from 'Connection.create_bucket'.
Merge pull request #321 from tseaver/159-document_exceptions_for_bucket_delete

Fix #159: Document exceptions (currently) raised from 'Bucket.delete'.
Merge pull request #323 from tseaver/244-rename-key_data_iterator-not_api

Fix #244: Rename key iterators to indicate they are implementation details of Key.
Rename upload/download methods to clarify directionality.

- 'set_contents*' -> 'upload'.

- 'get_contents* -> 'download'.

Original boto-like names retained as aliases per @jgeewax.

Fixes #148.