Feature Request: Add a non interactive mode

[rylarson]

It would be extremely useful if pik had a non-interactive mode, maybe a flag that would tell pik to automatically accept the default in cases where there is a default, and maybe choose a sensible default for other cases. For example:

pik install -y ruby 1.9.1 would automatically download the 7zip package instead of asking for it.

pik use -y ruby 2.0.0 would automatically choose the newest version of ruby 2.0 that is installed if there are more than one.

It might also be useful to have pik config interactive=false as a global configuration.