LaTeX reader: allow optional arguments on \footnote.

Closes #4062.

src/Text/Pandoc/Readers/LaTeX.hs

@@ -1337,8 +1337,8 @@ inlineCommands = M.union inlineLanguageCommands $ M.fromList $
   , ("bar", lit "|")
   , ("textless", lit "<")
   , ("textgreater", lit ">")
-  , ("thanks", note <$> grouped block)
-  , ("footnote", note <$> grouped block)
+  , ("thanks", skipopts >> note <$> grouped block)
+  , ("footnote", skipopts >> note <$> grouped block)
   , ("verb", doverb)
   , ("lstinline", dolstinline)
   , ("Verb", doverb)

test/command/4062.md

@@ -0,0 +1,6 @@
+```
+% pandoc -t latex
+Sentence blah.\footnote[][-.5in]{I'm a footnote}
+^D
+Sentence blah.\footnote[][-.5in]{I'm a footnote}
+```