convert razor_package_get_details() and razor_package_iterator_next() to varargs

The functions for getting package details about a package were limited to a few
things, when in the future we will want to support much more about a package.
The iterator was also limited to name,version,arch when most of the time we
didn't need all this data.

 prefix=@prefix@

 exec_prefix=@exec_prefix@

 libdir=@libdir@

 includedir=@includedir@

 Name: razor

 Description: library for depsolving, installing and removing packages

 Version: @VERSION@

 Requires: libcurl

 Libs: -L${libdir} -lexpat -lz -lrazor

 Cflags: -I${includedir}/razor