What's new since 0.5.4?

• Updated git to 2.26.2 for the helper.
• Improved experimental support for pushing merges.
• Fixed a few issues with experimental support for python 3.
• Don't complain the helper is outdated if it's newer.
• Auto-enable graft when cinnabarclone contains a graft that can be fulfilled.
• Exclude git-cinnabar notes and git-filter-branch backups from graft candidates.
• Graft failures are more now silent.
• Fixed handling of a null manifest.