Adding a simple .travis.yml that builds with gcc-5

.travis.yml

+sudo: required
+dist: trusty
+
+language: cpp
+
+env:
+  - C_COMPILER=gcc-5 CXX_COMPILER=g++-5
+
+before_install:
+  - sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
+  - sudo apt-get update -q
+  - sudo apt-get install gcc-5 g++-5 -y
+  - sudo apt-get install libboost-all-dev libeigen3-dev libopencv-dev -y
+
+before_script:
+  - mkdir build
+  - cd build
+  - cmake -DCMAKE_C_COMPILER=${C_COMPILER} -DCMAKE_CXX_COMPILER=${CXX_COMPILER} -DBUILD_EXAMPLES=on -DBUILD_UTILS=on ..
+
+script:
+  - make VERBOSE=1