Proposing a PR to fix a few small typos

# Issue Type

[x] Bug (Typo)

# Steps to Replicate and Expected Behaviour

- Examine couchdbkit/client.py, couchdbkit/schema/base.py and observe `attachement`, however expect to see `attachment`.
- Examine couchdbkit/client.py, couchdbkit/schema/base.py and observe `lenght`, however expect to see `length`.
- Examine couchdbkit/client.py and observe `securrity`, however expect to see `security`.
- Examine couchdbkit/client.py and observe `secuirity`, however expect to see `security`.
- Examine couchdbkit/schema/properties.py and observe `retireved`, however expect to see `retrieved`.
- Examine couchdbkit/schema/__init__.py and observe `pythoin`, however expect to see `python`.
- Examine couchdbkit/exceptions.py and observe `parsiing`, however expect to see `parsing`.
- Examine couchdbkit/resource.py and observe `parameterss`, however expect to see `parameters`.
- Examine couchdbkit/wsgi/proxy.py and observe `overrided`, however expect to see `overridden`.
- Examine couchdbkit/client.py and observe `optionnal`, however expect to see `optional`.
- Examine couchdbkit/ext/django/forms.py and observe `docuemnt`, however expect to see `document`.
- Examine doc/couchdbkit.org/htdocs/docs/api/epydoc.js and observe `becaue`, however expect to see `because`.
- Examine couchdbkit/client.py and observe `alows`, however expect to see `allows`.

# Notes

Semi-automated issue generated by
https://github.com/timgates42/meticulous/blob/master/docs/NOTE.md

To avoid wasting CI processing resources a branch with the fix has been
prepared but a pull request has not yet been created. A pull request fixing
the issue can be prepared from the link below, feel free to create it or
request @timgates42 create the PR. Alternatively if the fix is undesired please
close the issue with a small comment about the reasoning.

https://github.com/timgates42/couchdbkit/pull/new/bugfix_typos

Thanks.