Use slf4j to log.
Index#include? is O(1) instead of O(n).
Added index subcommand to list the index.
Fix for gems with duplicate executable entries.
Index#handled? delegates to Index#include?
Basic support for indexing metadata keys.
Index returns nil for non indexed metadata.
index subcommand prints out the N -> n-exts, U -> unresolved-dep, E -> Exception and A -> Added.