Merge_root option

[hendrikp]

Sometimes one has multiple repositories, and wants combined help for them.

The repositories might contain chapters that have to be inserted into the existing chapter hierarchy on root level.

This PR allows for that, up for discussion / change requests.

Sample:

Repo 1 (folder in docs/) SUMMARY.md:

General
    - Chapter1.md*

Repo 2 (folder in docs/) SUMMARY.md:

General
    - Chapter2.md*

Result

• General
  • Chapter1
  • Chapter2

(Also works on sub-levels, first occurrence determines order)