Update the CHANGELOG with format deprecation & fix info

CHANGELOG.rdoc

@@ -1,10 +1,14 @@
 = CHANGELOG
 
-== Unreleased (0.14.1)
+== Unreleased (0.15.0)
 
+* *DEPRECATION* When creating an `OEmbed::Provider` instance, specifying the format via positional argument is now deprecated. Please use a named argument instead: `OEmbed::Provider.new(@endpoint_url, format: :json)`
+* Fix Issue #77: Built-in Instagram & Facebook providers are now instances again.
+* Add support for `OEmbed::Provider` instances with `required_query_params` (like access tokens), where the provider will fail to answer until it is fully configured.
 
 == 0.14.0 - 5 November 2020
 
+* *BREAKING* Built-in providers for Instagram & Facebook are now classes, not instances, and therefore can't manually be registered via `OEmbed::Providers.register(OEmbed::Providers::Instagram)`; See Issue #77
 * Add support for Facebook/Instragram access tokens; Pull #75 (Inge Jørgensen)
 
 == 0.13.1 - 25 May 2020