[#12] config() returns wrong paths

The library path is made from concatenating per-dist
share directory, and sub-share directory, plus 'lib/',
plus library file name. But the 'lib/' directery was
omitted, so, base directory names and base file name was
correct but its absolute path was incorrect by missing
fragments of each paths.

This commit makes some changes to its API, yet its docu-
mentation is not authored.