Create HTML for http-protocol.txt

./Documentation/technical/http-protocol.txt was missing from TECH_DOCS in Makefile.
Add it and also improve HTML formatting while still retaining good readability of the ASCII text:
- Use monospace font instead of italicized or roman font for machine output and source text
- Use roman font for things which should be body text
- Use double quotes consistently for "want" and "have" commands
- Use uppercase "C" / "S" consistently for "client" / "server";
  also use "C:" / "S:" instead of "(C)" / "(S)" for consistency and
  to avoid having formatted "(C)" as copyright symbol in HTML
- Use only spaces and not a combination of tabs and spaces for whitespace

Signed-off-by: Thomas Ackermann <th.acker@arcor.de>
http-protocol.txt: don't use uppercase for variable names in "The Negotiation Algorithm"