doc: enable warnings as errors

This will let CI catch more problems. Fixes #104

Checking references had to be temporarily disabled because of temporarily disabled pages.

Makefile

@@ -2,7 +2,7 @@
 #
 
 # You can set these variables from the command line.
-SPHINXOPTS    =
+SPHINXOPTS    = -W
 SPHINXBUILD   = sphinx-build
 SPHINXPROJ    = Pybricks
 SOURCEDIR     = source
@@ -17,4 +17,4 @@ help:
 # Catch-all target: route all unknown targets to Sphinx using the new
 # "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).
 %: Makefile
-	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)

source/conf.py

@@ -86,7 +86,15 @@ language = None
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
 # This patterns also effect to html_static_path and html_extra_path
-exclude_patterns = []
+exclude_patterns = [
+    'motorcontrol.rst',
+    'signaltypes.rst',
+    'startinstall.rst',
+    'startrun.rst',
+]
+
+# TODO: remove this when pages above are added back in
+suppress_warnings = ['ref.ref']
 
 # The name of the Pygments (syntax highlighting) style to use.
 pygments_style = 'sphinx'