Fetch the submodules in readthedocs with ci_fetch_deps.py

.readthedocs.yml

@@ -12,11 +12,9 @@ build:
     os: ubuntu-20.04
     tools:
         python: "3"
-
-submodules:
-    include:
-        - extmod/ulab
-        - frozen
+    jobs:
+        post_install:
+            - python tools/ci_fetch_deps.py docs HEAD
 
 formats:
     - pdf

tools/ci_fetch_deps.py

@@ -68,7 +68,7 @@ submodules = []
 if target == "test":
     submodules = ["extmod/", "lib/", "tools/", "extmod/ulab", "lib/berkeley-db-1.xx"]
 elif target == "docs":
-    # NOTE: must match .readthedocs.yml as this script is not run by readthedocs
+    # used in .readthedocs.yml to generate RTD
     submodules = ["extmod/ulab/", "frozen/"]
 elif target == "mpy-cross-mac":
     submodules = ["tools/"]  # for huffman