[ci] Add Windows CI support, provided by AppVeyor (#308)

README

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+[![Build Status](https://ci.appveyor.com/api/projects/status/4oaq58ns2h0m2soa?svg=true)](https://ci.appveyor.com/project/behdad/harfbuzz)
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appveyor.yml

+platform: x64
+
+environment:
+  matrix:
+    - compiler: msvc
+      ARCH: amd64
+      CFG: release
+    - compiler: msvc
+      ARCH: x86
+      CFG: release
+    - compiler: msvc
+      ARCH: amd64
+      CFG: debug
+    - compiler: msvc
+      ARCH: x86
+      CFG: debug
+
+install:
+  - C:\msys64\usr\bin\bash -lc "pacman --noconfirm -S mingw-w64-x86_64-ragel"
+
+build_script:
+  - '"C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" %ARCH%'
+  - C:\msys64\usr\bin\bash -lc "cd $APPVEYOR_BUILD_FOLDER; PATH=$PATH:/mingw64/bin:/mingw32/bin; ./autogen.sh; make distdir"
+  - cd harfbuzz-*\win32
+  - nmake /f Makefile.vc CFG=%CFG% DIRECTWRITE=1
+
+# disable automatic tests
+test: off

win32/generate-msvc.mak

@@ -23,4 +23,4 @@ $(HB_GOBJECT_ENUM_GENERATED_SOURCES): ..\src\hb-gobject-enums.h.tmpl ..\src\hb-g
 
 # Create the build directories
 $(CFG)\$(PLAT)\harfbuzz $(CFG)\$(PLAT)\harfbuzz-icu $(CFG)\$(PLAT)\harfbuzz-gobject $(CFG)\$(PLAT)\util:
-	@-mkdir $@
+	@-mkdir -p $@