Optimize appveyor build

- AppVeyor does not run matrix builds in parallel, so creating a matrix with the intent to
  speed up the build will actually result in longer build times, as each matrix will execute
  in a brand new VM.
- tox does not detect 64 bit installations in AppVeyor, it always installs interpreters
  from C:\PythonX.Y, so there's no point to have 64bit builds
- No need for the auxiliary script "install.ps1" because all python versions we are interested
  in are already pre-installed in AppVeyor

appveyor.yml

@@ -1,98 +1,19 @@
-environment:
-  matrix:
-
-    # Pre-installed Python versions, which Appveyor may upgrade to
-    # a later point release.
-
-    - PYTHON: "C:\\Python27"
-      PYTHON_VERSION: "2.7.x" # currently 2.7.9
-      PYTHON_ARCH: "32"
-      TESTENV: "py27"
-
-    - PYTHON: "C:\\Python27-x64"
-      PYTHON_VERSION: "2.7.x" # currently 2.7.9
-      PYTHON_ARCH: "64"
-      TESTENV: "py27"
-
-    - PYTHON: "C:\\Python33"
-      PYTHON_VERSION: "3.3.x" # currently 3.3.5
-      PYTHON_ARCH: "32"
-      TESTENV: "py33"
-
-    - PYTHON: "C:\\Python33-x64"
-      PYTHON_VERSION: "3.3.x" # currently 3.3.5
-      PYTHON_ARCH: "64"
-      TESTENV: "py33"
-
-    - PYTHON: "C:\\Python34"
-      PYTHON_VERSION: "3.4.x" # currently 3.4.3
-      PYTHON_ARCH: "32"
-      TESTENV: "py34"
-
-    - PYTHON: "C:\\Python34-x64"
-      PYTHON_VERSION: "3.4.x" # currently 3.4.3
-      PYTHON_ARCH: "64"
-      TESTENV: "py34"
-
-    - PYTHON: "C:\\Python35"
-      PYTHON_VERSION: "3.5.x" # currently 3.5.0
-      PYTHON_ARCH: "32"
-      TESTENV: "py35"
-
-    - PYTHON: "C:\\Python35-x64"
-      PYTHON_VERSION: "3.5.x" # currently 3.5.0
-      PYTHON_ARCH: "64"
-      TESTENV: "py35"
-
-    # Also test a Python version not pre-installed
-    # See: https://github.com/ogrisel/python-appveyor-demo/issues/10
-
-    - PYTHON: "C:\\Python266"
-      PYTHON_VERSION: "2.6.6"
-      PYTHON_ARCH: "32"
-      TESTENV: "py26"
-
-    # xdist testing
-
-    - PYTHON: "C:\\Python27"
-      PYTHON_VERSION: "2.7.x" # currently 2.7.9
-      PYTHON_ARCH: "32"
-      TESTENV: "py27-xdist"
-
-    - PYTHON: "C:\\Python35"
-      PYTHON_VERSION: "3.5.x" # currently 3.5.0
-      PYTHON_ARCH: "32"
-      TESTENV: "py35-xdist"
-
-
 install:
-  - ECHO "Filesystem root:"
-  - ps: "ls \"C:/\""
+  - echo Installed Pythons
+  - dir c:\Python*
 
-  - ECHO "Installed SDKs:"
-  - ps: "ls \"C:/Program Files/Microsoft SDKs/Windows\""
-
-  # Install Python (from the official .msi of http://python.org) and pip when
-  # not already installed.
-  - ps: if (-not(Test-Path($env:PYTHON))) { & appveyor\install.ps1 }
-
-  # Prepend newly installed Python to the PATH of this build (this cannot be
-  # done from inside the powershell script as it would require to restart
-  # the parent CMD process).
-  - "SET PATH=%PYTHON%;%PYTHON%\\Scripts;%PATH%"
-
-  # Check that we have the expected version and architecture for Python
-  - "python --version"
-  - "python -c \"import struct; print(struct.calcsize('P') * 8)\""
-
-  # Install the build dependencies of the project. If some dependencies contain
-  # compiled extensions and are not provided as pre-built wheel packages,
-  # pip will build them from source using the MSVC compiler matching the
-  # target Python version and architecture
-  - C:\Python27\python -m pip install tox
+  - C:\Python35\python -m pip install tox
 
 build: false  # Not a C# project, build stuff at the test step instead.
 
 test_script:
-  # Build the compiled extension and run the project tests
-  - C:\Python27\python -m tox -e %TESTENV%
+  - 'set TESTENVS=
+          flakes,
+          py26,
+          py27,
+          py33,
+          py34,
+          py27-xdist,
+          py35-xdist
+    '
+  - C:\Python35\python -m tox -e "%TESTENVS%"