Add config file support to allow easy customization.

[eseglem]

Alternative to #2 which should be cross platform and easy for all users.

This does not add any additional dependencies, yaml is built in.

I attempted to break the yml file with notepad and wordpad and was unable to, so I believe this might be a good alternative to environment variables while avoiding users editing the Vagrantfile.

[andymccurdy]

This is probably easier than environment variables for most users, especially Windows folks.

However I could see it causing problems in the future for non-technical users. Specifically they could run into merge conflicts if they tweak a value, build their VM, and then in the future attempt to update their git repo to the newest version.

We should probably just provide zip/tar.gz downloads of this repo and communicate that in the README/documentation as the preferred way to get the code so we don't have to teach users git.

[eseglem]

I was actually thinking about that issue, because I have a different location for the directory and it is a pain to not update that file, and change branches, etc. The solution, I believe, is actually move vagrant_config.yml to vagrant_config_example.yml and add vagrant_config.yml to gitignore. This would just mean the user has to make a copy of example, edit it, and not have any conflicts. The only risk of that is adding options later which are not included in their config.