invoke ocamlc through ocamlfind
Merge pull request #190 from fdopen/windows

add windows support
AppVeyor: basic build configuration.
AppVeyor: patch findlib to use Unix.system instead of Unix.create_process

Unix.create_process fails with status 127 under Cygwin.
AppVeyor: build and run the tests.
use mingw ocaml
add wget
extract archive at the right location
AppVeyor: change libffi install location.
add 64-bit test
indiciate test success with exit status
create include directory
cleanup first
Add an AppVeyor status badge to the README.