Launchdarkly-server-sdk

Changed
- Better error handling when sending events.

Changed
- Now using jsonpickle to serialize analytics events. Addresses https://github.com/launchdarkly/python-client/issues/57
- Better handling of indirect/put and indirect/patch messages in streaming connection.

Added
- Twisted support for LDD mode only.

Changed
- FeatureStore interface get() and all() methods now take an additional callback parameter.

Added
- Support for multivariate feature flags. `variation` replaces `toggle` and can return a string, number, dict, or boolean value depending on how the flag is defined.
- New `all_flags` method returns all flag values for a specified user.
- New `secure_mode_hash` function computes a hash suitable for the new LaunchDarkly [JavaScript client's secure mode feature](https://github.com/launchdarkly/js-client#secure-mode).

Deprecated
- The `toggle` call has been deprecated in favor of `variation`.

Removed
- Twisted support has temporarily been removed.