Makes the build system to look for yajl using a macro file

Now searching for yajl using find_yajl.m4 macro file instead
of using pkg-config directly. If YAJL was not found or if it
was disabled in the configure phase, the code will be compiled
without JSON support.
Supports the yajl version 2

Initially the code was made to support the yajl version 1. The
version 2 is now the default option in most of Linux distributions.
Adds support to JSON parser in the nginx module

Building with --enable-standalone-module was failing due
the lack of the reference to the msc_json.c file inside the
standalone/Makefile.am. This patch also place the dependency
of the yajl to the nginx module config script.
Adds JSON support on ISS port

The JSON parse is already supported in Nginx and Apache
versions. This patch adds support on the IIS port.