(www url-coding) module provides two procedures for decoding
and encoding URL strings for safe transmission according to RFC 1738.
Return a new string made from url-decoding str. Specifically,
+ into space, and hex-encoded
%XX strings into
their eight-bit characters.
Return a new string made from url-encoding str, unconditionally transforming those in reserved-chars, a list of characters, in addition to those in the standard (internal) set.