Add Dockerfile to build/run examples

The version of boost pre Ubuntu 20.04 does not does not have full
float128 support. The Dockerfile will set up an environment in which:

  - C++, Java, Python 3.8, and Rust examples can be run
  - Boost 1.73.0 is available
  - hyperfine is available for benchmarking
  - A basic install of vim and zsh are available
  - C++ and Rust code have been compiled
  - Various testing (e.g., pyhamcrest) and linting tools (e.g., cpplint)
    are available