Add 2 custom handlers:
1. roam-file?file=path: this simply opens the file at path in Emacs.
2. roam-ref?ref=ref&template=roam-template&title=title&...: attempts to open a roam note with a given ROAM_KEY. If the note doesn't exist, create one. Else, open it.
All org-roam related information will now be stored in the database. Henceforth, the cache needs to be built synchronously once (via `M-x org-roam-build-cache`), which is then incrementally updated.
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 "./"))))))
* fix org-roam--parse-content incorrect :to computation
org-roam--parse-content always computed the to-path relative to the
org-roam-directory, when it should be relative to the file-path in
question. Fixes#81.
* Add to changelog
