Use python 3.3 in appveyor

Author: abnerfs

.appveyor/build.bat

@@ -1,7 +1,7 @@
 @echo on
 call "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" x86
 mkdir opt32 && cd opt32
-C:\python27\python.exe ..\configure.py --enable-optimize
+python ..\configure.py --enable-optimize
 ambuild
 cd ..
 opt32\dist\testrunner.exe

.appveyor/setup_environment.bat

@@ -1,6 +1,7 @@
 @echo on
+SET PYTHON=c:\python33
+SET PATH=%PYTHON%;%PYTHON%\Scripts;%PATH%
 git submodule update --init
 git clone https://github.com/alliedmodders/ambuild ambuild
-cd ambuild
-c:\python27\python.exe setup.py install
+pip install ./ambuild
 chdir /D "%APPVEYOR_BUILD_FOLDER%"