Update appveyor to build both 32 bit and 64 bit versions of love for Windows.

--HG--
branch : minor

extra/appveyor/appveyor.yml

@@ -4,9 +4,18 @@ image: Visual Studio 2013
 
 shallow_clone: true
 
+environment:
+  matrix:
+    - PLATFORM: x86
+      VCVARSALL_PLATFORM: x86
+      GENERATOR: "Visual Studio 12"
+    - PLATFORM: x64
+      VCVARSALL_PLATFORM: x86_amd64
+      GENERATOR: "Visual Studio 12 Win64"
+
 init:
 # Make VS 2013 command line tools available
-- call "C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\vcvarsall.bat" %platform%
+- call "C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\vcvarsall.bat" %VCVARSALL_PLATFORM%
 
 install:
 # We need to install NSIS to create the packaged installer executable.
@@ -26,7 +35,7 @@ install:
 - move love libs\love
 
 before_build:
-- cmake -G "Visual Studio 12" -H. -Bbuild
+- cmake -G "%GENERATOR%" -H. -Bbuild
 
 build_script:
 - cmake --build build --target PACKAGE --config Release