'/?&#' -> '/?#' and '?&#' -> '?#'
According to https://www.ietf.org/rfc/rfc3986.txt, URLs are
"organized hierarchically" by using "the slash ("/"), question
mark ("?"), and number sign ("#") characters to delimit components"
Child extractors are now directly constructed with Extractor.from_url()
if the extractor class is known beforehand, instead of using
extractor.find() and searching through all possible extractor classes.
The former implementation would produce a complete list of all subalbums
for each (sub)album extraction. This would for example result in a
level 2 subalbum getting "extracted" twice: once through the root-album
(level 0) and once through its parent album on level 1.
In the current implementation only the next level of subalbums are
returned, which themselves will handle their next level in a recursive
fashion.
