url: make notmuch query string parser generic (#812)

url: make notmuch query string parser generic (#812)

* Notmuch: remove custom UriTag linked list

Use STAILQ helper for UriTag linked list.

* url: make notmuch query string parser generic

Enhance the url.c to handle query strings.

This permits to remove the notmuch custom url parser.

* url: always parse query string

This removes url_parse_with_qs methods.

* fix some problems

- double free in nm_normalize_uri()
- set path to NULL in url_parse()
  If we're setting all the other members, we should set the path too
- tidy some doxygen docs

* notmuch: remove useless starting / from db_filename