Add HTTP field value parsers:

ext_list:
    Iterable container of comma separated extensions, where each extension
    is a token followed an optional list of semicolon delimited parameters,
    with each parameter consisting of a name / value pair. The value can
    be a token or quoted-string.

param_list:
    Iterable container of semicolon delimited parameters, where each parameter
    is a name / value pair. The value can be a token or quoted-string.

token_list
    Iterable container of comma delimited tokens.

* Remove obsolete rfc2616 functions

* Refactor and consolidate case-insensitive string helpers

test/Jamfile

@@ -54,7 +54,6 @@ unit-test http-tests :
     http/read.cpp
     http/reason.cpp
     http/resume_context.cpp
-    http/rfc2616.cpp
     http/rfc7230.cpp
     http/status.cpp
     http/streambuf_body.cpp