Added AppVeyor CI.

Change-Id: I01cf630026e25382b585785b471bad21153338f6

appveyor.yml

+branches:
+  only:
+    - master
+
+os: Visual Studio 2015
+
+platform:
+  - x86
+  - x64
+
+configuration:
+  - Debug
+  - Release
+
+before_build:
+  - cmake -G"Visual Studio 10 2010"
+
+build:
+  project: ALL_BUILD.vcxproj
+
+#test_script:
+#  - Debug/flattests.exe
+
+#artifacts:
+#  - path: Release/flatc.exe
+#    name: flatc.exe

readme.md

-![logo](http://google.github.io/flatbuffers/fpl_logo_small.png) FlatBuffers [![Build Status](https://travis-ci.org/google/flatbuffers.svg?branch=master)](https://travis-ci.org/google/flatbuffers) 
+![logo](http://google.github.io/flatbuffers/fpl_logo_small.png) FlatBuffers
 ===========
+[![Build Status](https://travis-ci.org/google/flatbuffers.svg?branch=master)](https://travis-ci.org/google/flatbuffers) [![Build status](https://ci.appveyor.com/api/projects/status/yg5idd2fnusv1n10?svg=true)](https://ci.appveyor.com/project/gwvo/flatbuffers)
+
 **FlatBuffers** is an efficient cross platform serialization library for games and
 other memory constrained apps. It allows you to directly access serialized data without
 unpacking/parsing it first, while still having great forwards/backwards compatibility.