Fix __parse_connection()

Multiple connection tokens may be present at the same time in
the "Connection:" header. Important tokens are processed explicitly,
while other are processed in a generic way. Should the need arise,
tokens can be added to the explicit processing section (for instance,
the "TE" token).
Fix incorrect handling of "other" headers in tfw_http_parse_resp()

- The 'p' pointer was reset to a possibly NULL value, and then used
  in a check. Do not reset the 'p' pointer. Also, the move forward
  was for a wrong number of bytes.
- Use uniform variable names and code constructs when searching for
  a LF, CR, comma, or space characters.
- Reformat several identical comments for better readability.
"keep-alive" and "close" tokens may not be present at the same time

These two connection tokens are mutually exclusive. Enforce that
when processing the "Connection:" header in __parse_connection().
Incorrect use of "len" throughout http_parser.c

CHUNK_STRNCASECMP() is used in functions and parts of the code to find
and process specific HTTP headers and header tokens (fields). The macro
uses "len" argument that is set once in each function prior to the macro
use. As the macro is used and the FSM moves from one state to another,
the "p" pointer is moved forward as well, thus making the initial "len"
value no longer correct. Using the initial "len" value may therefore
lead to memory corruption.

- Fix CHUNK_STRNCASECMP() macro.
- Fix all places that use the initial "len" value.
- Fix several places where a "comma" pointer is incorrectly compared
  to an "lf" pointer (similar to 46f3eaeb)
- Correct a small number of comments for consistency and readability.
- Use the same naming conventions in macros as in the rest of the code.
Add support for HTTP/1.0

It's still out there, mostly in requests. Responses go out as HTTP/1.1.