Started to describe alex_2 changes. The follwoing entries were added to

Started to describe alex_2 changes. The follwoing entries were added to
ChangeLog. These are some of the low level changes coming from  thealex_2 branch.

        - Replaced _http_reply with HttpReply. HttpReply is a stand-alone object
          that is responsible for parsing, swapping, and comm_writing of HTTP
          replies. Moved these functions from various modules into HttpReply
          module.

        - Added HttpStatusLine, HttpHeader, HttpBody.

        - All HTTP headers are now parsed and stored in a "compiled" form in the
          HttpHeader object.  This allows for a great flexibility in header
          processing and builds basis for support of yet unsupported HTTP headers.

        - Added Packer, a memory/store redirector with a printf interface.  Packer
          allows to comm_write() or swap() an object using a single routine.

        - Added MemBuf, a auto-growing memory buffer with printf capabilities.
          MemBuf replaces most of old local buffers for compiling text messages.

        - Added MemPool that maintains a pre-allocated pool of opaque objects.
          Used to eliminate memory thrashing when allocating small objects (e.g.
          field-names and field-value in http headers).