restructure library documentation

docs/library/NominatimAPI.md

@@ -0,0 +1,38 @@
+# The Nominatim API classes
+
+The API classes are the core object of the search library. Always instantiate
+one of these classes first. The API classes are **not threadsafe**. You need
+to instantiate a separate instance for each thread.
+
+### NominatimAPI
+
+::: nominatim.api.NominatimAPI
+    options:
+        members:
+            - __init__
+            - config
+            - close
+            - status
+            - details
+            - lookup
+            - reverse
+            - search
+            - search_address
+            - search_category
+        heading_level: 6
+        group_by_category: False
+        show_signature_annotations: True
+
+
+### NominatimAPIAsync
+
+::: nominatim.api.NominatimAPIAsync
+    options:
+        members:
+            - __init__
+            - setup_database
+            - close
+            - begin
+        heading_level: 6
+        group_by_category: False
+        show_signature_annotations: True