[REQ] Ability to synchronise req-cnts between wiki and code

[mhatzl]

mantra must have a command to automatically update ref-cnts in the wiki.
Updating these cnts manually would not be feasible.

Preferably a GitHub action should be available that updates the wiki on every push to the branch the action is set to.
However, it should also be possible to synchronise ref-cnts for local projects and wikis.

[mhatzl]

Wiki pages are simple markdown files in GitHub, so there are no property fields counts can be attached to.
As a result, some syntax rules must be adhered to by users for mantra to correctly find and update ref-cnts in the wiki.

The best way I could come up with so far is a bullet list with **References:** above it, which is directly below the heading of the requirement.

Example:

# my_req: Some Title

**References:**

- in branch main: 3
- in branch stable: 1

The branches should also have links pointing to the branch in the repository.

[mhatzl]

Requirements will be traced using a requirements ID set in the wiki section.
To allow hierarchical requirement structures, the ID of sub-requirements must follow the form parent_reg_id.sub_req_id.
As consequence, a . in an ID is only allowed if requirement IDs exist for all parent ID-parts.

[mhatzl]

Syntax for references on the code side will be [req:your_req_id].
This should be distinctive enough from common expressions in most programming languages.

[mhatzl]

This issue was partially implemented in v0.1.0.

The GitHub action will take more time, and is moved to the separate issue #11