Update API links

Author: ghutchis

.github/workflows/build.yml

@@ -59,3 +59,4 @@ jobs:
       with:
         github_token: ${{ secrets.GITHUB_TOKEN }}
         publish_branch: gh-pages
+        cname: openbabel.org

source/api/index.md

@@ -1,10 +1,10 @@
 (api)=
 # API
 
-The latest version of the API documentation is [3.0](3.0/) 
+The latest version of the API documentation is [3.0](/api/3.0/) 
 
 Older API docs for historical purposes
-- [2.3](2.3.0/index.html)
-- [2.2](2.2.0/index.html)
-- [2.1](2.1.0/index.html)
-- [2.0](2.0.2/index.html)
+- [2.3](/api/2.3.0/index.html)
+- [2.2](/api/2.2.0/index.html)
+- [2.1](/api/2.1.0/index.html)
+- [2.0](/api/2.0.2/index.html)