Added high-level tests for dict and multi_dict.
Added high-level tests for dict and multi_dict.

These unit tests assume that the contents of QueryString.dict and
QueryString.multi_dict will be based on the results of QueryString.list;
therefore it's not necessary to repeat all the encoding tests applied to
.list.

zacharyvoase/urlobject,agriffis/urlobject,vartagg/urlblocks