Allow skipping things based on env vars #10
Description
It would be nice to be able to disable things individually with environment variables.
For example: set ADP_RUBY=0 to disable installation of rbenv and Ruby.
Then it would be trivial to get something highly customized just by adding a shell script to set all the variables you care about (for example, maybe you only need .NET on the dev machine and don't care about anything else, so you skip Ruby, Node, Python, etc.).