Doomsday Engine

Uri|Optimize|Refactor: Various de::Uri refactorings

Reimplemented Uri's resolved() algorithm, making use of QStringRef
and C++ exceptions. The revised expression parser addresses most
of the design and suboptimal performance issues in the previous
iteration and is also more tolerant of syntax errors (e.g, missing
closing brackets no longer result in fatal error (though a warning
is logged)).

Began switching the rest of de::Uri's API to use de::String rather
than ddstring_t. As a C wrapper API is still necessary, the path()
and scheme() methods return ddstring_t pointers presently. (it may
be necessary to cache the composed path as ddstring_t in addition
to the resolved path).

Also fixed a bug in ResourceNamespace::addSearchPath() resulting
in search paths being resolved unnecessarily.