- use '?a.hitomi.la' as subdomain depending in gallery-id
- add 'characters', 'tags' and 'date' information
- support multiple entires per metadata-value
- rename 'num' to 'page'
This commit mostly replaces all minus-signs ('-') in keyword names with
underscores ('_') to allow them to be used in filter-expressions. For
example 'gallery-id' got renamed to 'gallery_id'.
(It is theoretically possible to access any variable, regardless of its
name, with 'locals()["NAME"]', but that seems a bit too convoluted if
just 'NAME' could be enough)
