Gitman

- Updated default arguments to `Source` model for improved library usage.
- Added support for multiple symbolic `links` per repo. (gunechristensen)
- **WARNING**: `link` may be deprecated in a future release.
- Added support for virtual drives on Windows. (gunechristensen)
- Updated scripts installation to be depth-first. (mrpossoms)

- Fixed working tree validation to ignore case. (sch0125)
- Fixed handling of empty directories as checkout locations. (Erich-McMillan)
- Fixed `list` command to handle missing dependencies.
- Added an option to specify a default group. (Erich-McMillan)
- Fixed `install` command to handle both groups and sources. (brandonaut)
- Fixed deletion of the project directory when `location: .` is used.

- Added realtime display of shell calls. (spurnvoj)

- **BREAKING**: Removed legacy `gdm` CLI entry point.
- **BREAKING**: Dropped support for Python 3.6.
- Switched to `datafiles` for YAML serialization.

- Added support Python 3.8.

- **BREAKING**: Renamed `-f` alias to `-F` (`-f` now implies `--force-interactive`).
- Added `--force-interactive` option to interactively overwrite changed dependencies on install or update command. (daniel-brosche)
- Added basic group support. (daniel-brosche)
- Improved validity check of git repo. (mttjohnson)
- Added rebuilding missing repo on `install --force`. (mttjohnson)
- Added support for symlinks on Windows. (sergey-shuyskiy)