Reduce bloat.

Reduce bloat.

Expat can call CharacterData() multiple times if the CDATA contains
entity references.  We need to collect all of them in one large
string.

Reduce bloat.

Eliminate the std::string bloat.

Reduce runtime bloat.

Reduce overhead by omitting the part of the buffer that consists only
of whitespace.

Replaces "m_title" and "m_props".  More bloat removed.

Reduce bloat.

There is no use in duplicating these containers.  It only means that
we have to search both, duplicating the code.

Call titleToPathElt() only once for each object.

"upnp:class" is an element, not an attribute of element "item".  This
fixes a regression from commit 65ebfb16

Don't add to the std::map.

Don't store in the std::map.

Don't put all <res/> attributes to the attributes map; parse the
"duration" attribute as soon as we receive it, and store it in an
integer attribute.  This reduces bloat.

Look up attributes in the "atts" array.  Reduce bloat.

Reduce bloat.

Reduce bloat.

Reduces bloat.

We only need it inside StartElement().  Reduces bloat.

No need to handle this in EndElement() - in StartElement(), we already
have all we need.

Reduce excessive bloat.

At the same time, rename the enum types and the class attributes, and
add an "UNKNOWN" type/class.  The latter avoids the "-1" hack.

[mk: renamed source files, applied coding style, reduced bloat, using
MPD's threading library, using MPD's error reporting and logging
library and refactoring, fixed lots of bugs]