refactor code to be more modular and add passing tests

[millzpaugh]

This PR:

• Adds a Makefile for docker builds
• Refactors code in a modular way so it can be used to download all mason packages or a single package
• Adds bash commands Add cli commands  #11
  • mason-js install which installs all packages from the mason-versions.ini file
  • mason-js install <package>=<version> --type=<package type>
  • mason-js install protozero=1.5.1 --``type=header
• Adds a bash help command
• Adds a test suite Create a test suite #8 for:
  • file reader
  • CLI commands
  • downloading & placing binary

Note: This suite does NOT add tests for symlinking - still needs to be added

cc @springmeyer