Bump version to 0.8.1
- Use manually set IDG_VERSION for PACKAGE_VERSION instead of GIT_TAG
- Bump version to 0.8.1 to indicate support for Stokes I only mode
The GIT_TAG mechanism is left as is, only the exported version number (PACKAGE_VERSION) now comes from a manually defines IDG_VERSION number. This is the minimal change needed to signal new functionality to wsclean, without creating a new tag.
The subminor version was bumped to indicated support for new functionality without breaking old functionality. (In team Schaap we bump the minor version for breaking changes).