Feature parity with vim-rooter

[DzedCPT]

Todos:

• Implement vim-rooter's logic for matching the root of a project. Currently nvim-rooter only matches files by names.
• Implement rooter_targets config field.
• Implement rooter_change_directory_for_non_project_files
• Add function to change workdir to current current file's path or project root. A function for each and a toggling between the two would be good.
• vim-rooter provides a get_root_dir vim command, which should also be added here.