RTDs: Fail on warning

Fix outstanding sphinx warnings;
- Change mycells.lib to use `text` parsing instead of (currently) unsupported `Liberty`.
- Remove unused `troubleshooting.rst`, moving the todo into the index.

.readthedocs.yaml

@@ -13,6 +13,7 @@ formats:
 
 sphinx:
   configuration: docs/source/conf.py
+  fail_on_warning: true
 
 python:
   install:

docs/source/using_yosys/more_scripting/index.rst

@@ -3,6 +3,8 @@ More scripting
 
 .. todo:: brief overview for the more scripting index
 
+.. todo:: troubleshooting document(?)
+
 .. toctree::
    :maxdepth: 3
 

docs/source/using_yosys/more_scripting/troubleshooting.rst

@@ -1,6 +0,0 @@
-Troubleshooting
-~~~~~~~~~~~~~~~
-
-.. todo:: troubleshooting document(?)
-
-See :doc:`/cmd/bugpoint`

docs/source/using_yosys/synthesis/cell_libs.rst

@@ -90,8 +90,10 @@ Mapping to hardware
 For this example, we are using a Liberty file to describe a cell library which
 our internal cell library will be mapped to:
 
+.. todo:: find a Liberty pygments style?
+
 .. literalinclude:: /code_examples/intro/mycells.lib
-   :language: Liberty
+   :language: text
    :linenos:
    :name: mycells-lib
    :caption: :file:`mycells.lib`