Makefiles for automating the Windows build.

* TODO:
  - document: how to use
  - known bugs/shortcomings
  - separate the configurable parts to a Makefile.local.tmpl file
  - allow serf,httpd,neon,etc to be optional
  - auto-generate the list of individual targets from build.conf
    (that list is not used by the default make targets)
  - add 'make tools' to the default windows build

See: http://svn.haxx.se/users/archive-2009-07/0764.shtml
(Message-Id: <alpine.561.2.00.0907241718550.6824@daniel2.local>)
