Version 0.4.0

Cache - Possible breaking change

All cache have lost the timeout parameter in set() method.
If you have a custom cache with timeout, you should remove it, as it will not allow the Etag process to be used. If you keep it with a default value, it will continue to work.

Do not cache POST, PUT and DELETE requests anymore
Support for head requests
Add Etag mechanism in the cache management
Allow to set a raise_on_error flag in EsiClient.request() to get an exception when status is not 2XX.
Add a timeout value for requests in the EsiClient.__init__() to force timeout requests (default is None)
Allow to define a custom Signal to replace API_CALL_STATS using signal_api_call_stats when initializing the client.

Allow to define a custom Signal to replace AFTER_TOKEN_REFRESH using signal_token_updated when initializing the client.
Add a token identifier that will be returned to the AFTER_TOKEN_REFRESH signal listeners, so it can identify a token

Added request_param and response_header to the Exception, to have more precise data for error management

cache_time parameter value has changed. Number and 0 will still behave like before (forcing a cache time or no expiration with 0), None will disable forced cache time and use Expires header from swagger specifications. Default is still 1d caching.
While getting swagger spec (meta or any version), EsiApp will make sure to deal correctly with caching (headers Expires and Etag) by doing a HEAD request before (due to how App object works).
Add a datasource argument on initialization, to be able to get swagger spec for specific datasource (tranquility by default, or singularity)