Documentation update.
A number of changes were made to improve the quality of the documentation.
- Added a License file. This replaces the body of the License section of the README.md. The license itself is unchanged.
- Added badges to the README.md to indicate the version number of the current release, the license type and an indicator that the releases are signed using Gnu Privacy Guard (GPG).
- Added a new section to the README.md, Verifying Releases, which details how release tags are signed and how they can be verified to ensure the integrity of the repo.
- In previous releases I have only increased the version number when there has been functional (non-documentation) changes made to the repo but from this version on I will bump the version up even if only documentation has changed.