* HTTP request logging

In addition to six built-in log formats, you can define your own
"named" formats and use them in the LogLevel directive.  Log format is
defined using the following statement:

  LogFormat "name" "format_string"

The "name" argument specifies a string uniquely identifying this
format.  "Format_string" is the format specification.  It is
modelled after Apache's mod_log_config LogFormat string.  For example,
the built-in format 3 is defined as:

  "%a - %u %t \"%r\" %s %b \"%{Referer}i\" \"%{User-Agent}i\""

The LogLevel directive has been extended to take symbolic format name
as argument.  For example:

  LogLevel "my_format"

The traditional built-in formats are assigned the following symbolic names:

  0 - "null"
  1 - "regular"
  2 - "extended"
  3 - "vhost_combined"
  4 - "combined"
  5 - "detailed"

So, instead of

  LogLevel 3

one may write

  LogLevel "vhost_combined"

* New statements: ForwardedHeader and TrustedIP

These statements control how the %a log format conversion specifier
determines the originator IP address:

  ForwardedHeader "name"
    Defines the name of HTTP header that carries the list of
    proxies the request has passed through.  It is used to
    report the originator IP address when logging.

    The default is "X-Forwarded-For".  This statement can be
    used in global, listener, and service scope.

  TrustedIP
    Defines a list of trusted proxy IP addresses, which is used to
    determine the originator IP.  This is a special form of the ACL
    statement and, as the latter, it can appear in two forms: directive
    and section.

    In directive form, it takes a single argument referring to a
    named access control list, which must have been defined previously
    using the ACL statement.

    In section form, it is followed by a list of one or more CIDRs
    each appearing on a separate line.  The End directive on a
    separate line terminates the statement.

    This statement can be used in global, listener, and service scope.

* New service statement: LogSuppress

Suppresses HTTP logs for requests that resulted in response status
codes from a particular group or groups.  The statement takes one or more
arguments specifying status code groups to suppress log messages for:

  info or 1      1xx status codes
  success or 2   2xx status codes
  redirect or 3  3xx status codes
  clterr or 4    4xx status codes
  srverr or 5    5xx status codes
  all            all status codes

Suggested usage is for special services that are likely to accept
large numbers of similar requests, such as Openmetrics services.  For
example:

   Service "metrics"
       URL "/metrics"
       Metrics
       LogSuppress success
   End

* New request matching directive: StringMatch

The syntax is:

  StringMatch "SUBJECT" [OPTIONS] "PATTERN"

OPTIONS are usual matcher options.  The directive matches if SUBJECT,
after backreference expansion and accessor interpretation, matches
PATTERN.

This directive allows you to build complex service selection criteria.
For example:

  Service
      Host "^foobar\.(.+)$"
      StringMatch "$1" -file "domain.list"
      ...
  End

The service above will be used for requests whose Host header value is
"foobar." followed by a domain name from the file "domain.list".

* New request accessors: host and port

The %[host] accessor returns the hostname part of the Host header
value.  The %[port] accessor returns port number with leading
column character.  If no explicit port number is given in the Host
value, %[port] returns empty string.

* Bugfixes

** Fix the QueryParam statement.

** Improve testsuite and documentation.