Remove unneeded code from the MySQL example

The `boxen?` method isn't used anywhere in the file. Remove it so that there's less code for people to copy and paste and to generate less confusion as to why there's a method there that doesn't need to be there.
Add sample hiera configuration
Add note about the module cache
Mention the default hiera configuration in README
Suggest some example hierarchies
Be explicit that puppet-module-data is important
Added boxen upgrade instructions
Added more detailed update process
Moved Upgrading instructions to FAQ
fixed spelling error
Update README.md

Other boxem fixed.