add Travis CI support

Use a matrix of 4 jobs, linux (ubuntu trusty), mingw i686, mingw x86-64
and mac.

Automatically detect ccache in the cmake config and cache the
`~/.ccache` directory for faster rebuilds.

Instructions for ccache in cmake are here:
https://stackoverflow.com/a/24305849

Change build status badge in README.md to Travis.

.travis.yml

@@ -0,0 +1,55 @@
+---
+sudo: required
+
+cache:
+    directories:
+        - "$HOME/.ccache"
+
+matrix:
+    fast_finish: true
+    include:
+        - env: BUILD_ENV=ubuntu
+          language: cpp
+          os: linux
+          dist: trusty
+          before_script:
+              - ./installdeps
+          script:
+              - mkdir build
+              - cd build
+              - cmake ..
+              - make -j2
+#              - ./visualboyadvance-m --help
+        - env: BUILD_ENV=mingw-w64
+          language: cpp
+          os: linux
+          dist: trusty
+          before_script:
+              - ./installdeps MinGW-w64-x86_64
+          script:
+              - mkdir build
+              - cd build
+              - /usr/lib/mxe/usr/bin/x86_64-w64-mingw32.static-cmake ..
+              - make -j2
+        - env: BUILD_ENV=mingw-w32
+          language: cpp
+          os: linux
+          dist: trusty
+          before_script:
+              - ./installdeps MinGW-w64-i686
+          script:
+              - mkdir build
+              - cd build
+              - /usr/lib/mxe/usr/bin/i686-w64-mingw32.static-cmake ..
+              - make -j2
+        - env: BUILD_ENV=mac
+          language: cpp
+          os: osx
+          before_script:
+              - ./installdeps
+          script:
+              - mkdir build
+              - cd build
+              - cmake ..
+              - make -j2
+#              - ./visualboyadvance-m.app/Contents/MacOS/visualboyadvance-m --help

CMakeLists.txt

@@ -38,6 +38,13 @@ endif()
 
 set(ASM_DEFAULT OFF)
 
+# use ccache if available
+find_program(CCACHE_FOUND ccache)
+if(CCACHE_FOUND)
+    set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE ccache)
+    set_property(GLOBAL PROPERTY RULE_LAUNCH_LINK ccache)
+endif(CCACHE_FOUND)
+
 if(NOT CMAKE_SYSTEM_PROCESSOR)
     if(NOT CMAKE_TOOLCHAIN_FILE AND CMAKE_HOST_SYSTEM_PROCESSOR)
         set(CMAKE_SYSTEM_PROCESSOR ${CMAKE_HOST_SYSTEM_PROCESSOR})

README.md

@@ -15,7 +15,8 @@
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
 
 [![Join the chat at https://gitter.im/visualboyadvance-m/Lobby](https://badges.gitter.im/visualboyadvance-m/Lobby.svg)](https://gitter.im/visualboyadvance-m/Lobby)
-[![Build Status](https://tea-ci.org/api/badges/visualboyadvance-m/visualboyadvance-m/status.svg)](https://tea-ci.org/visualboyadvance-m/visualboyadvance-m)
+[![Build Status](https://travis-ci.org/visualboyadvance-m/visualboyadvance-m.svg?branch=master)](https://travis-ci.org/visualboyadvance-m/visualboyadvance-m)
+
 # Visual Boy Advance - M
 
 Game Boy Advance Emulator