SurveyGizmo version 0.2.0

Forwards incompatible changes:

• Renamed the 'change' operations to 'update'. This is consistent with SurveyGizmo's API naming.
• Removed the 'keep' kwarg for preserving filters bettween api funcion calls. This is now configured with 'preserve_filters'. Filters are now cleared manually with api.clear_filters()
• Removed the undocumented 'url_fetch' kwarg, which prevented api executioned and instead returned the prepared url.

Backwards incompatible changes:

• Modified 'api_version' to no longer has any effect on the client. SurveyGizmo provides no way to meaningfully differentiate between API versions, so this checking was unneeded and created code duplication
• Added 'prepare_url' as a replacement for 'url_fetch'. This forces the client to return the url after being prepared instead of executing the api call. This is useful in cases where you need to call the api asynchronously.
• Added 'requests_kwargs'. These are additional arguments passed to requests.get. Useful for setting timeouts and otherwise configuring the requests library.
• Added handling for CloudFlare 52x errors