also build on appveyor

appveyor.yml

@@ -0,0 +1,25 @@
+version: 1.18.2-develop+{build}
+branches:
+  only:
+  - master
+  - develop
+  - /^release/
+  - /^appveyor/
+  - /^build-ci/
+image:
+- Visual Studio 2017
+- Visual Studio 2015
+build_script:
+- cmd: >-
+    if "Visual Studio 2017"=="%APPVEYOR_BUILD_WORKER_IMAGE%" call "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvars64.bat"
+      if "Visual Studio 2015"=="%APPVEYOR_BUILD_WORKER_IMAGE%" call "C:\Program Files\Microsoft SDKs\Windows\v7.1\Bin\SetEnv.cmd" /x64
+      if "Visual Studio 2015"=="%APPVEYOR_BUILD_WORKER_IMAGE%" call "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" x86_amd64
+      cd..
+      git clone https://github.com/libtom/libtommath.git --branch=master
+      cd libtommath
+      nmake -f makefile.msvc
+      cd..
+      cd libtomcrypt
+      nmake -f makefile.msvc all
+test_script:
+- cmd: test.exe