HTML parser class

Changes for 3.82 - 2024-03-13

• "img lowsrc" and "body background" are not in the HTMLv5 spec (GH#43) (Jess)
• Replace "FileHandle" with "IO::File" (GH#42) (James Raspass)
• Fix some minor typos (GH#41) (Yoshikazu Sawa)