add configuration for AppVeyor

Like Travis CI, only compilation is checked with MSVC 2013 (32-bit)
and MSVC 2015 (64-bit).

appveyor.yml

@@ -0,0 +1,18 @@
+version:      "{build}"
+clone_folder: c:\wkhtmltopdf
+test:         off
+
+environment:
+  matrix:
+    - TARGET: msvc2013-win32
+    - TARGET: msvc2015-win64
+
+install:
+  - git submodule update --init --recursive --force --depth 50
+  - perl -p -i.bak -e "s/quiet = 0/quiet = 1/g" qt/bin/syncqt
+
+build_script:
+  - scripts\build.py %TARGET%
+
+artifacts:
+  - path: static-build\wkhtmltox*.exe