simplify() is written to process incoming plaintext messages
and extract footers and quotes from them.
Incoming messages contain various quote styles
and simplify() implements heuristics to detects them.
If dehtml() output is processed by simplify(),
simplify() heuristics may erroneously detect
footers and quotes in produced plaintext.
dehtml() should directly detect quotes
instead of converting them to plaintext quotes
for parsing with simplify().
