TST: Build configuration for Appveyor (Windows builds)

The included appveyor.yml is set up to run tests for Windows on Miniconda Python 2.7, 3.4 and 3.5. Someone from the project would need to set up an Appveyor account and switch it on for the project.

Merge also includes a fix for a dcotest where the default int type on windows meant that the repr of an array was different from the expected repr as it explicitly shows the dtype.

Builds are automatically integrated with the Gitlab builds, and example of a passing build. https://ci.appveyor.com/project/tdaff/ase/build/1.0.17 (along with several failing builds)

See also #39 (closed)