Add missing modules to API docs build.

Includes tweaks to Sphinx config and module files to help the docs build.

Reviewed the docs build with:
sphinx-build -E -W -b html . _build/html

docs/conf.py

@@ -19,7 +19,14 @@ extensions = [
 # Uncomment the below if you use native CircuitPython modules such as
 # digitalio, micropython and busio. List the modules you use. Without it, the
 # autodoc module docs will fail to generate with a warning.
-autodoc_mock_imports = ["machine", "Adafruit_GPIO", "RPi", "RPi.GPIO", "hid", "sysv_ipc"]
+autodoc_mock_imports = [
+    "machine",
+    "Adafruit_GPIO",
+    "RPi",
+    "RPi.GPIO",
+    "hid",
+    "sysv_ipc",
+]
 
 intersphinx_mapping = {
     "python": ("https://docs.python.org/3.4", None),

src/pulseio.py

@@ -30,4 +30,4 @@ elif detector.board.greatfet_one:
 elif "sphinx" in sys.modules:
     pass
 else:
-    raise NotImplementedError("pulseio not supported for this board.")
+    raise NotImplementedError("pulseio not supported for this board.")