[SR-15312] [Swift-DocC] Add 'version' command to docc command line tool

[ethan-kusters]

Previous ID	SR-15312
Radar	rdar://58842647
Original Reporter	@ethan-kusters
Type	Bug
Status	Closed
Resolution	Invalid

Additional Detail from JIRA

Votes	1
Component/s	Swift-DocC
Labels	Bug, StarterBug
Assignee	None
Priority	Medium

md5: 765556f0235e43786ce452dab96df62e

Issue Description:

docc should output it's current version to the command line.

This could be similar to the behavior of the `swift --version` command and output the current version of `docc` along with a commit hash.

[swift-ci]

Comment by Adin Cebic (JIRA)

Hello @ethan-kusters I tried implementing "version" command and hit some opstacles and drew possible conclusion why such command was not built in the first place.

Firstly, readme.md file in swift-docc repository states following:

> Swift-DocC's CLI tool ( docc) will be integrated into the Swift toolchain and follows the Swift compiler's versioning scheme.

So what ever the current Swift version is, you can assume that it is the same for docc CLI.

Secondly, there is no obvious place to write current docc version since SPM promotes using git tags for that. In case of this CLI, no git tags are created by project maintainers.