changelog: add missing summary messages

Summary messages for versions 1.7.0 and 1.8.0 were missed. The patch
adds messages.

Related to #220

CHANGELOG.md

@@ -41,6 +41,8 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
 
 ## [1.8.0] - 2022-08-17
 
+The minor release with time zones and interval support for datetime.
+
 ### Added
 
 - Optional msgpack.v5 usage (#124)
@@ -55,6 +57,11 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
 
 ## [1.7.0] - 2022-08-02
 
+This release adds a number of features. The extending of the public API has
+become possible with a new way of creating requests. New types of requests are
+created via chain calls. Streams, context and prepared statements support are
+based on this idea.
+
 ### Added
 
 - SSL support (#155)