CI: try adding appveyor

[ev-br]

Borrow .appveyor.yml from numpy.

[ev-br]

Build started
git clone -q https://github.com/ev-br/sparr.git C:\projects\sparr
git fetch -q origin +refs/pull/20/merge:
git checkout -qf FETCH_HEAD
Specify a project or solution file. The directory does not contain a project or solution file.

whatever this means :-(.
OK, disable AppVeyor for now.