Provide Windows binaries

[ickc]

Related to #9.

Reference: https://packaging.python.org/appveyor/

Reason: Most Unix system has Python2 preinstalled (Mac may requires an update on pip though), but not Windows.

If so, this gives #9 more reason to have all listed there as dependencies, so that potentially the end users only need to install pandoc and pandocpm (pypandoc even included pandoc, if we choose to list it as a dependency too), at least for simple/pip filters.

[ickc]

From JessicaTegner/pypandoc#106: bundling pandoc into the wheel is not easy. The last option (that pandocpm includes pandoc) should not be considered. If effort is to be made, it should be made to pypandoc and list that into the dependencies of pandocpm.

[jankatins]

Note that pypandoc now (again) includes windows wheels with pandoc inside: https://github.com/bebraw/pypandoc/blob/master/appveyor.yml