Merge pull request #26 from jgorset/requests

Merge pull request #26 from jgorset/requests

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Ive implemented a `settings` context manager as described in [pull request #25](https://github.com/kennethreitz/requests/pull/25#issuecomment-1039541).

    >>> import requests
    >>> with requests.settings(timeout=0.5):
    ...     requests.get(http://example.org) # Times out after 0.5 seconds
    ...     requests.get(http://example.org, timeout=10) # Times out after 10 seconds

Settings may also be manipulated separately:

    >>> import requests
    >>> requests.timeout = 0.5
    >>> requests.get(http://example.org) # Times out after 0.5 seconds