releaser.sh: ensure that templates for obsolete components are deleted

Also includes:
- Comments added
- More output added to template-library-core update
- Removal of unneeded 'git push' in update_config_file()

Fixes #29
`REPOS_PARENT_DIR` doesn't exist, `RELEASE_ROOT` does, but you should already be in the right place and could just do `cd template-library-examples` in the same way that the other functions do.