Each org-roam-directory gets its own cache. One can override the `org-roam-directory` variable locally via dir-locals:
((org-mode . ((eval . (setq-local org-roam-directory (expand-file-name "./"))))))
Makes org-roam-mode a global minor mode. This mode adds an advice to find-file-function, which decides whether to turn on the local post-command-hook and after-save-hook.
It also advices delete-file and rename-file to ensure cache consistency. Also fixes a bug introduced with #142
