Makefile: fix
add jsonm to META
Merge pull request #1751 from ygrek/fix_makefile

Makefile: fix
Add an experimental Appveyor Windows/Cygwin32 build file

This uses the Appveyor CI service (similar to Travis) to build
OPAM on Cygwin on Windows.  It currently installs fine, but then
runs into ocsigen/lwt#84 when installing Lwt.

See ocaml/opam#246