Heavy LdCanvas refactoring, some modifications to ld-types.
It just wasn't possible for me to further work with an old,
2000 lines long file without shuffling everything around
at the same time.
This is required for gtkdoc-scangobj. So far it's much like it's been
before, the main differences are that source files are in two directories
from now on and the build process has two stages.
