README: add changelog and bump version

[ci skip]

README.md

@@ -907,6 +907,10 @@ Note that there is also http://quickdocs.org/string-case/.
 
 ## Changelog
 
+* 0.21, November, 2023:
+  * added the `regex` key argument to `split`, `rsplit`, `split-omit-nulls`.
+* August, 2023:
+  * added the `regex` key argument to the `replace-*` functions.
 * March, 2023:
   * added `str:ensure`, `str:ensure-prefix`, `str:ensure-suffix`, `str:ensure-wrapped-in` and `str:wrapped-in-p`.
 * January, 2023: added the `:char-barg` parameter to `trim`, `trim-left`, `trim-right`.

str.asd

@@ -4,7 +4,7 @@
   :author "vindarel <[email protected]>"
   :maintainer "vindarel <[email protected]>"
   :license "MIT"
-  :version "0.19.1"
+  :version "0.21"
   :homepage "https://github.com/vindarel/cl-str"
   :bug-tracker "https://github.com/vindarel/cl-str/issues"
   :source-control (:git "[email protected]:vindarel/cl-str.git")