Focus on currently supported versions of CPython

Drop Python 2.6 which reached its end of life more than five years ago and 3.4 which will reach its end of life in less than 50 days.  https://devguide.python.org/#status-of-python-branches

Also implements some of the good ideas from ogrisel#41

appveyor.yml

@@ -3,69 +3,47 @@ environment:
     # SDK v7.0 MSVC Express 2008's SetEnv.cmd script will fail if the
     # /E:ON and /V:ON options are not enabled in the batch script intepreter
     # See: http://stackoverflow.com/a/13751649/163740
-    CMD_IN_ENV: "cmd /E:ON /V:ON /C .\\appveyor\\run_with_env.cmd"
+    CMD_IN_ENV: cmd /E:ON /V:ON /C .\appveyor\run_with_env.cmd
 
   matrix:
 
-    # Python 2.7.10 is the latest version and is not pre-installed.
-    # Python versions: https://www.appveyor.com/docs/build-environment/#python
+    # Build images: https://www.appveyor.com/docs/build-environment/
+    # Python versions: https://www.appveyor.com/docs/windows-images-software/#python
+    # Legacy Python 2.7.15 is the latest version and is pre-installed.
 
-    - PYTHON: "C:\\Python27.10"
-      PYTHON_VERSION: "2.7.10"
-      PYTHON_ARCH: "32"
-
-    - PYTHON: "C:\\Python27.10-x64"
-      PYTHON_VERSION: "2.7.10"
-      PYTHON_ARCH: "64"
-
-    # Pre-installed Python versions, which Appveyor may upgrade to
-    # a later point release.
-    # See: http://www.appveyor.com/docs/installed-software#python
-
-    - PYTHON: "C:\\Python27"
-      PYTHON_VERSION: "2.7.x" # currently 2.7.9
-      PYTHON_ARCH: "32"
-
-    - PYTHON: "C:\\Python27-x64"
-      PYTHON_VERSION: "2.7.x" # currently 2.7.9
-      PYTHON_ARCH: "64"
-
-    - PYTHON: "C:\\Python33"
-      PYTHON_VERSION: "3.3.x" # currently 3.3.5
-      PYTHON_ARCH: "32"
+    - PYTHON: C:\Python27
+      PYTHON_VERSION: 2.7.x
+      PYTHON_ARCH: '32'
 
-    - PYTHON: "C:\\Python33-x64"
-      PYTHON_VERSION: "3.3.x" # currently 3.3.5
-      PYTHON_ARCH: "64"
+    - PYTHON: C:\Python27-x64
+      PYTHON_VERSION: 2.7.x
+      PYTHON_ARCH: '64'
 
-    - PYTHON: "C:\\Python34"
-      PYTHON_VERSION: "3.4.x" # currently 3.4.3
-      PYTHON_ARCH: "32"
+    # Python versions, which Appveyor may upgrade to later point releases.
 
-    - PYTHON: "C:\\Python34-x64"
-      PYTHON_VERSION: "3.4.x" # currently 3.4.3
-      PYTHON_ARCH: "64"
+    - PYTHON: C:\Python37
+      PYTHON_VERSION: 3.7.x
+      PYTHON_ARCH: '32'
 
-    # Python versions not pre-installed
+    - PYTHON: C:\Python37-x64
+      PYTHON_VERSION: 3.7.x
+      PYTHON_ARCH: '64'
 
-    # Python 2.6.6 is the latest Python 2.6 with a Windows installer
-    # See: https://github.com/ogrisel/python-appveyor-demo/issues/10
+    - PYTHON: C:\Python36
+      PYTHON_VERSION: 3.6.x
+      PYTHON_ARCH: '32'
 
-    - PYTHON: "C:\\Python266"
-      PYTHON_VERSION: "2.6.6"
-      PYTHON_ARCH: "32"
+    - PYTHON: C:\Python36-x64
+      PYTHON_VERSION: 3.6.x
+      PYTHON_ARCH: '64'
 
-    - PYTHON: "C:\\Python266-x64"
-      PYTHON_VERSION: "2.6.6"
-      PYTHON_ARCH: "64"
-
-    - PYTHON: "C:\\Python35"
-      PYTHON_VERSION: "3.5.0"
-      PYTHON_ARCH: "32"
+    - PYTHON: C:\Python35
+      PYTHON_VERSION: 3.5.x
+      PYTHON_ARCH: '32'
 
-    - PYTHON: "C:\\Python35-x64"
-      PYTHON_VERSION: "3.5.0"
-      PYTHON_ARCH: "64"
+    - PYTHON: C:\Python3t-x64
+      PYTHON_VERSION: 3.5.x
+      PYTHON_ARCH: '64'
 
     # Major and minor releases (i.e x.0.0 and x.y.0) prior to 3.3.0 use
     # a different naming scheme.