Intents

Add:

* (19) Add basic SnipsNLU Connector
* (19) Add builtin entities module and `service_connector.PatchEntityMapping`
* Add `Color`, `Language`, `MusicGenre` and `FirstName` builtin entities
* (19) Add `EntityMapping.supported_languages` property
* (17) Add Fulfillment interface with support for Dialogflow, Alexa and Snips
* (17) Add dataclass model for Dialogflow Responses, Webhook requests and
Webhook responses
* (17) Add dataclass model for Alexa Fulfillment requests and responses
* (17) Implement recursive local fulfillment for Snips and Alexa
* (17) Implement development fulfillment server
* (16) Add configurable intent lifespan
* (16) Add `new_lifespan` property to `follow` relation

Change:

* (11) Breaking change: remove deprecated `Context` interface, `Intent.events`
and `Intent.parameter_schema()` (`Intent.parameter_schema` is the way to
access that information)
* (16) Breaking change: replace `relations.related_intents()` with
`relations.intent_relations()` (without deprecation)
* (19) Change ServiceConnector to accept `LanguageCode` values as language
codes, in addition to ISO strings
* (17) Change (with deprecation) `Prediction.fulfillment_messages()` to be a
property of type `IntentResponseDict`. Remove
`Prediction.fulfillment_response_dict` (with deprecation)
* (17) Move `service_connector` to `connectors.interface` (with deprecation)
* (17) (internal) Refactor `ServiceEntityMappings` handling of Custom Entities
* (17) (internal) Refactor Dialogflow prediction modules:
* `connectors.dialogflow_es.response_format` renamed to `prediction_format`
* `DialogflowIntentResponse` classes moved from `prediction_format` to
`prediction`
* Replace protobuf parameters with dataclass equivalents
* Change Dialogflow context/event names generation to use CamelCase ->
snake_case conversion (e.g. context for `AskCoffee` will be `c_ask_coffee`
instead of `c_askcoffee`). This requires re-uploading old agents.

Fix:

* (19) Enforce name constraints on Entities
* (17) Fix Entity export in Dialogflow (canonical value needed to be in
synonyms as well)
* (17) Patch entity entries with invalid characters in Alexa
* Fix Webhook status and Image Response in Dialogflow `DetectIntent` payload parsing

This release contains breaking changes (see [semantic versioning FAQ](https://semver.org/#doesnt-this-discourage-rapid-development-and-fast-iteration)), they are reported below.

* (4) Add experimental Alexa connector
* (7) Add `follow` intent relation
* (7) Deprecate manual Contexts
* (7) Breaking change: predict() and trigger() now return Prediction objects
* (5) Change documentation to render pages separately
* (9) Change Intent and Agent model to enforce stricter naming rules
* (10) Change `Intent.parameter_schema()` to `Intent.parameter_schema` (with deprecation)
* (10) Fix double dataclass decorator bug
* (13) Fix Entities de-serialization during predictions

First release, includes

* **Model** for basic Agent Definition
* Intents with parameters, default parameters and List parameters
* System Entities
* Custom Entities
* Input/Output contexts
* **Language** Resources implementation
* Example Utterances with parameter references
* Slot filling prompts
* Text responses
* Rich responses (Quick Replies, Image, Card and Custom Payloads)
* Multi-language support
* **Dialogflow ES** connector
* Export Agent as ZIP
* Upload Agent to Cloud project
* Make *predict* requests
* Make *trigger* requests