DOC: Fix Sphinx warnings surfaced by the documentation gate

Lengthen a short title underline, lex the FFT output block as text,
and exempt doxygenclass lookups for classes absent from the current
nightly InsightDoxygen XML.

Author: hjmjohnson

CMake/CTestCustom.cmake.in

@@ -46,6 +46,9 @@ set(CTEST_CUSTOM_WARNING_EXCEPTION
   "LabelGeometryImageFilter.*deprecated"
   "note: declared here"
   "RemovedInSphinx[0-9]+Warning"
+  # Nightly InsightDoxygen XML is currently missing these classes upstream.
+  "doxygenclass: Cannot find class"
+  "Could not find match for .itk::"
   "ipo: warning #11053"
   "ipo: warning #11053"
   "vxl.core.vnl.algo"

src/Core/Common/ReadAPointSet/Documentation.rst

@@ -52,7 +52,7 @@ C++
    :lines: 18-
 
 WebAssembly
-......
+...........
 
 .. literalinclude:: WebAssembly.html
    :language: html

src/Filtering/FFT/ComputeFFTInOneDimension/Documentation.rst

@@ -39,7 +39,9 @@ Results
 
   Output Phase Image
 
-Output::
+Output:
+
+.. code-block:: text
 
   Read real input image of type <class 'itk.itkImagePython.itkImageF2'> and size itkSize2 ([1536, 128])
   Padded input image to size itkSize2 ([1536, 128])