Feature request: Add new type 'vcs' for g:startify_lists

Nobody has claimed this yet.

I have `let g:startify_change_to_vcs_root = 1` and thought I could list all recent files from that VCS project like so:
```vim
let g:startify_lists = [
\ { 'type': 'dir', 'header': [' Recent files in project '. fnamemodify(getcwd(), ':t')] },
\ ]
```
But `getcwd()` is not _vcs_root_ but the current directory (suppose I am in a subfolder of the project).

Suggestion add an additional type `'vcs'` (instead of `'dir'` here) that lists recent files from the latest edited VCS project.

Start by locating the handling for g:startify_lists and the existing 'dir' type, then inspect how g:startify_change_to_vcs_root affects the current directory. Define the expected behavior for a new 'vcs' list type that uses the latest edited VCS project, and verify the resulting recent-file list against a project subfolder scenario.

Written by the indexing model from the issue text.