Generate docs for CLI flags

[yurishkuro]

Resolves #250 , replaces #263 and #257

[yurishkuro]

Changes since @lucperkins 's PR #263:

• flag description is rendered as a separate row, to make the tables more readable (no wrapping of most flags). I also dropped "shortcut" column since we usually don't define those for all flags
• removed documentation for docs, env, and version commands, as there's not a lot of value in those (we could add them if desired, but the page is already pretty long).
• created a data/cli/${ver]/config.json that describes which tools the docs should be generated for and which storage options are applicable to each tool. Both the templates and the script that generates YAML files use that config as the main index. Later versions can run with a different config, e.g. if we add new storage options.
• YAML files generated for all applicable storage types

Strictly speaking, the PR can be merged as is already, as it gives usable docs. But the following could be improved:

• as @objectiser mentioned, it would be better to use tabs for different storage options, as otherwise the page becomes really long (booked Improve rendering of CLI flags with tabs #267)
• the right-hand sidebar menu is too long and does not fit / does not scroll. If we switch to tabs for storage types, the sidebar menu will be much smaller and manageable (booked Improve rendering of CLI flags with tabs #267)
• the tables could use some styling so that the flag descriptions are not separated by dividers
• the next-version does not generate CLI docs because the script only stores the YAML files under versioned data/cli dir. TBD how to handle that, as well as the overall cutting of a new release, which currently requires copying at least the config.json and cli.md files. (booked Incorporate CLI Flags documentation generation in cutting a new release #268)

[yurishkuro]

@pavolloffay @objectiser @jpkrohling do we want to merge this as is? The only real issue is that the right sidebar is partially unusable (but navigation is also available from the top of the page).

[objectiser]

Fine with me. Having the information available is a benefit and formatting can be improved later.

[yurishkuro]

ok, I removed the right sidebar completely, since it's not fully usable, and added some in-page navigation. Need approval to merge.

[pavolloffay]

great to see this landing here. Thanks @lucperkins @yurishkuro !