Stacked Git 0.23

Stacked Git v0.23 is primarily a bug fix release that corrects
several bugs found in v0.22 along with several other longstanding
issues.

Removed

• Drop support for Python 3.3; Python 2 (2.6 and 2.7) remain deprecated, but supported for one last release
• Tutorial is removed; it now exists as part of the website

Deprecated

• Python 2.x support is deprecated and will be removed in a future release

Added

• Support html5 output of docs from asciidoc
• Add --expose option for stg pick to allow picked commit message to be customized

Changed

• Limit mail diffstat to 72 columns
• Added pyproject.toml file for black configuration
• Minimum Git version is 2.2.0
• Quote stg and subcommand in man page synopsis
• Replaced RELEASENOTES with this CHANGELOG.md
• Replaces Documentation/SubmittingPatches with CONTRIBUTING.md

Fixed

• Repair MANIFEST.in and generated source dist
• Repair importing mail with ": " (colon space) in subject
• Fix mail cover letter shortlog
• Fix mail cover letter diffstat
• stg series now only outputs colors when isatty()
• Repair mail SSL check (#57)
• Repair stg mail with both -a and -e options (#58)
• Remove empty short-opt for --no-submodules of stg refresh
• Repair build.py for Python 2 with explicit flush()
• stgit.refreshsubmodules added to sample gitconfig

Internal

• Update docs build system from upstream Git docs
• Use coverage contexts to map commands to covered lines
• Improve mail tests
• Use GitHub Actions instead of TravisCI
• Format StGit source using black formatter