There is no need to go through methods, signals, and properties in
two loops and only collect interfaces in the first run. Get rid of
unnecessary CPU use by generating the XML data for interfaces with
a single pass.
The XML used in D-Bus introspection is simple and there is no need to use
libxml2 to generate it. This gets rid of the dependency on the large
library by using internal XML generation.
Simpler to use for loops instead of handling next pointer selection
in all places. In addition, couple of functions could have ended up
in an infinite loop on error path since the pointer update was missed.
