examples: Move example1 camera slightly closer

Parameterise image class and generate main()

Make object and light vectors const

Use output stream to print Image class

examples: Use std::array in example1

Make object and light vector pointers const

examples: Increase example2 DoF samples

rt::render: Use references or out-pointers

renderer: Use reference for scene

Image: Use std::vector<> to store pixel data

Add local emacs variables

Use class for Pixel and std::ostream for printing

Update comment since LLVM has '__GNUC__'

Add "rt/" to header include paths

Makefile: parallelise by default