LaTeX reader: Allow _ and ^ as regular inline text.

Normally these will cause an error in LaTeX, but there
are contexts (e.g. `alltt` environments) where they are
okay.  Now that we aren't treating them as super/subscript
outside of math mode, it seems okay to parse them as regular
text.

src/Text/Pandoc/Readers/LaTeX.hs

@@ -824,7 +824,7 @@ inlineText :: LP Inlines
 inlineText = str <$> many1 inlineChar
 
 inlineChar :: LP Char
-inlineChar = noneOf "\\$%^_&~#{}^'`\"‘’“”-[] \t\n"
+inlineChar = noneOf "\\$%&~#{}^'`\"‘’“”-[] \t\n"
 
 environment :: LP Blocks
 environment = do