Specify version (ranges) for dependencies

Atomicwrites and vobject are more or less abandoned and did not have a
release in a long time.  They are pinned to exact versions in case some
change upstream results in an unexpected release.

For the other packages I took a guess what a good version constraint
could be.  They are not thoroughly tested and I did not study the
release notes to check which version we need.

pyproject.toml

@@ -23,11 +23,11 @@ keywords = ["vcard", "console", "addressbook"]
 license = {text = "GPL"}
 
 dependencies = [
-    "atomicwrites",
-    "configobj",
-    "ruamel.yaml",
-    "unidecode",
-    "vobject"
+    "atomicwrites == 1.4.1",
+    "configobj == 5.*, >= 5.0.6",
+    "ruamel.yaml >= 0.17.0",
+    "unidecode ~= 1.3.0",
+    "vobject == 0.9.6.1",
 ]
 
 [project.optional-dependencies]