* main: (39 commits)
Add '--version' flag to Help output (#1707)
Expose ValidateRequiredFlags and ValidateFlagGroups (#1760)
Document option to hide the default completion cmd (#1779)
ci: add workflow_dispatch (#1387)
add missing license headers (#1809)
ci: use action/setup-go's cache (#1783)
Adjustments to documentation (#1656)
Rename Powershell completion tests (#1803)
Support for case-insensitive command names (#1802)
Deprecate ExactValidArgs() and test combinations of args validators (#1643)
Use correct stale action `exempt-` yaml keys (#1800)
With go 1.18, we must use go install for a binary (#1726)
Clarify SetContext documentation (#1748)
ci: test on Golang 1.19 (#1782)
fix: show flags that shadow parent persistent flag in child help (#1776)
Update gopkg.in/yaml.v2 to gopkg.in/yaml.v3 (#1766)
fix(bash-v2): activeHelp length check syntax (#1762)
fix: correct command path in see_also for YAML doc (#1771)
build(deps): bump github.com/inconshreveable/mousetrap (#1774)
docs: add zitadel to the list (#1772)
...
* Move man_docs and md_docs into new doc pkg
* Replace *bytes.Buffer with io.Writer
* Replace c == cmd.helpCommand with c.IsHelpCommand()
* Remove redundant len(children) == 0 check in HasSeeAlso
* Duplicate test setup for doc generation
