* Provide defines and variables for version string components: major
version; minor version; patch level version; development suffix.
* Change commit date format to strict ISO.
* Add define/variable for Arbor build configuration.
* Add usage/help info to `git-source-id` script.
* Add define/variable for a full build identification string,
incorporating source info, version, build configuration, feature
options.
* Add documentation for the version and build defines and variables.
* Extend version unit tests to suit.