Pg-schema-version

- be stricter about backslash command detection
- improve documentation

- add `reverse` command to allow going backwards, and tests
- add `history` command to show application history of changes
- keep step execution history
- differentiate exit status depending on the error
- add `--version` option
- check app and hash option values
- keep executed commands and session users
- add debug mode
- fix `psv` command parsing

- make psv comment header (`-- psv: foo +1 …`) mandatory, including many sanity checks about names, versions…
- rename `run` to `apply`
- show status only when asked
- add `--partial` option to allow partial scripts (i.e. missing versions)
- use `--app` to check script consistency
- check current status strictly before applying a step
- improve documentation, esp. the example
- improve tests about descriptions
- refactor script sources

- add unregister and catchup commands
- add setting a version target for a run
- add filename and description fields
- add verbose option
- show description on status
- escape schema and table identifiers
- refactor application registration
- improve documentation

- activate GitHub pages
- working GitHub CI
- add coverage check
- add markdown check
- use exit code 3 for output file

- initial beta release for testing.