Re-implmented pr KSP-KOS#2339 because forked repo gone?

The repository in the PR is marked as "unknown", meaning
it might have been removed after the PR was made.  So
instead I'm implementing what was in the PR by re-typing it.

doc/ksdomain.py

@@ -12,7 +12,8 @@
 from sphinx.domains import Domain, ObjType, Index
 from sphinx.directives import ObjectDescription
 from sphinx.util.nodes import make_refnode
-from sphinx.util.compat import Directive
+# ### Next line is deprecated, and it seems to work without it, as per kOS PR #2339 ###
+# from sphinx.util.compat import Directive
 from sphinx.util.docfields import Field, GroupedField, TypedField
 
 ks_sig_re = re.compile(r'''