V1.17

• A CUDA testing environment with Docker and native OSX testing have been added to Travis CI.
• Changed Dockerfile to use a multi-stage build.
• Added Dockerfile for building CUDA into ffmpeg with nvidia/cuda container. (cuda-ubuntu.dockerfile)
• The indentation was unified to Tab and re-indent.
• Changed the config option (--enable-*) to be added in each build section (CONFIGURE_OPTIONS).
• Removed some config options because they were redundant.

Thanks @AkashiSN, PR: #56