Fix how end of paragraph is identified when parsing \code and
\verbatim blocks that appear within a paragraph and contain an empty
line. Previously this would generate a warning for unexpected end of
doxygen comments, and it could generate a segfault due to
dereferencing an invalid iterator value.
The doxygen_basic_translate.i and doxygen_basic_translate_style2.i
tests have been updated to serve as regression tests for this
behavior. Prior to this fix, inclusion of the empty code block line
in this context produced a segfault.
Missing returns resulted in test suite failures now that it is built with
-Wreturn-type, so avoid them by simply making most of the functions void and
adding explicit return statements to a couple of them that used Doxygen
\return command in their documentation, which doesn't make sense for the void
functions.
