Adding AppVeyor CI.

Initial stab at it.
Forgot to change name in appveyor.yml.
Fixed syntax error in install.ps1
Removed python-coveralls since it breaks stuff.
Pass python to conda add channel command.
Added PATH in messy way.
Added PATH in less messy way.
Make a conda environment on appveyor.
Replaced wrong variable for activate in appveyor.yml
Trying other variables combination.
Debugging.
Change path.
Fix typo in install.ps1
Edit path.
Debug.
Debug.
My powershell-fu is weak.
More debugging.
More debugging.
Removed spaces from install.ps1