This commit changes the source and documentation to reference this project as
`puppet-strings` rather than `puppetlabs-strings`.
This makes the source and project match the gem name.
Since puppet strings is a very small project, at the moment we
don't need to maintain a master and a stable branch. As a result,
the COMMITTERS.md guide should not contain references to the stable
branch or include information around dealing with both the master
and stable branch. Remove these references so that COMMITTERS is
consistent with our approach to the strings repository.
In order to make contributions more accessible to the community,
add COMMITTERS.md and CONTRIBUTING.md so that there are instructions
and resources for those who would like to contribute to the strings
module.