Added Mac Travis build steps

.travis.yml

     - if [ "$TRAVIS_OS_NAME" = "linux" ]; then cmake/travis_install_linux.sh; fi
     - if [ "$TRAVIS_OS_NAME" = "osx" ]; then cmake/travis_install_mac.sh; fi
 
-before_script:
-    - if [ "$TRAVIS_OS_NAME" = "linux" ]; then cmake/travis_before_script_linux.sh; fi
-    - if [ "$TRAVIS_OS_NAME" = "osx" ]; then cmake/travis_before_script_mac.sh; fi
-
 script:
-    - (mkdir build && cd build && cmake .. && make)
+    - if [ "$TRAVIS_OS_NAME" = "linux" ]; then cmake/travis_script_linux.sh; fi
+    - if [ "$TRAVIS_OS_NAME" = "osx" ]; then cmake/travis_script_mac.sh; fi
 
 notifications:
     irc:

cmake/travis_before_install_mac.sh

 #!/bin/bash
 
+brew update
 

cmake/travis_before_script_mac.sh

-#!/bin/bash
-
-

cmake/travis_install_mac.sh

 #!/bin/bash
 
+brew install sdl2 sdl2_ttf freealut cmake
 

cmake/travis_before_script_linux.sh → cmake/travis_script_linux.sh

 if [ "$CC" = "gcc" ]; then export CC="gcc-4.8"; fi
 if [ "$CXX" = "g++" ]; then export CXX="g++-4.8"; fi
 
+mkdir build && cd build && cmake .. && make
+

cmake/travis_script_mac.sh

+#!/bin/bash
+
+mkdir build && cd build && cmake .. && make
+