message: Add custom Travis builds for modern GCC and Clang
diff: @@ -2,17 +2,37 @@ language: cpp
  matrix:
  include:
  + # Standard Linux builds
  - os: linux
  - dist: trusty
  compiler: gcc
  - os: linux
  - dist: trusty
  compiler: clang
  +
  + # Standard OSX builds
  - os: osx
  compiler: gcc
  - os: osx
  compiler: clang
  + # Custom Linux builds
  + - os: linux
  + compiler: gcc
  + env: MATRIX_EVAL="CC=gcc-7 && CXX=g++-7"
  + addons:
  + apt:
  + sources: ubuntu-toolchain-r-test
  + packages: g++-7
  + - os: linux
  + compiler: clang
  + env: MATRIX_EVAL="CC=clang-5.0 && CXX=clang++-5.0"
  + addons:
  + apt:
  + sources: llvm-toolchain-trusty-5.0
  + packages: clang-5.0
  +
  +before_install:
  + - eval "${MATRIX_EVAL}"
  +
  script:
  - mkdir build
  - cd build
  