doc: upgrade deprecated sphinx features.

doc/conf.py

@@ -29,7 +29,7 @@
 # Add any Sphinx extension module names here, as strings. They can be extensions
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
 extensions = [
-    'sphinx.ext.pngmath',
+    'sphinx.ext.imgmath',
     'sphinx.ext.autodoc',
     'sphinx.ext.doctest',
     'sphinx.ext.autosummary',
@@ -199,11 +199,23 @@
 
 # -- Options for LaTeX output --------------------------------------------------
 
-# The paper size ('letter' or 'a4').
-#latex_paper_size = 'letter'
+latex_elements = {
+    # The paper size ('letterpaper' or 'a4paper').
+    #
+    # 'papersize': 'letterpaper',
 
-# The font size ('10pt', '11pt' or '12pt').
-#latex_font_size = '10pt'
+    # The font size ('10pt', '11pt' or '12pt').
+    #
+    # 'pointsize': '10pt',
+
+    # Additional stuff for the LaTeX preamble.
+    #
+    'preamble': '\setcounter{tocdepth}{3}',
+
+    # Latex figure (float) alignment
+    #
+    # 'figure_align': 'htbp',
+}
 
 # Grouping the document tree into LaTeX files. List of tuples
 # (source start file, target name, title, author, documentclass [howto/manual]).
@@ -226,16 +238,11 @@
 # If true, show URL addresses after external links.
 #latex_show_urls = False
 
-# Additional stuff for the LaTeX preamble.
-latex_preamble = '\setcounter{tocdepth}{3}'
-
 # Documents to append as an appendix to all manuals.
 #latex_appendices = []
 
 # If false, no module index is generated.
-#latex_domain_indices = True
-
-latex_use_modindex = False
+latex_domain_indices = False
 
 # -- Options for manual page output --------------------------------------------