I found that the strict heirarchy was not satisfying the situation
where one tag is the intersection of two others, but we can only
pick one as the parent
For example, does red_jacket belong under clothes.red_clothes or
clothes.jackets? A search for "red_clothes AND jackets" might
give us someone wearing red pants and a black jacket, so this
definitely needs to be a separate tag, but picking only one
parent for it is not sufficient. Now, a search for red_clothes
and a search for jackets will both find our red_jacket photo.
The change also applies to Albums because why not, and I'm sure
a similar case can be made.
Unfortunately this means tags no longer have one true qualname.
The concept of qualnames has not been completely phased out but
it's in progress.
This commit is very big because I was not sure for a long time
whether to go through with it, and so much stuff had to change
that I don't want to go back and figure out what could be grouped
together.
It was getting difficult to remember which of the normalizers
use None and which don't. So let's try to be a little more consistent
and just use empty sets, etc, so the caller can rely on receiving a
set instead of having to check for None.
Also renamed search parameter authors->author to be more in line
with the singular form of extension.
In order to achieve tag_musts, we break each of the musts down
into separate EXISTS queries for each of the matchable children.
Then we INTERSECT those, and finally do other filtering and
ordering as usual.
Previously they were relative to the directory from which the client
was launched, meaning it usually started with ./_etiquette.
Now it should be more portable and less tight.
