Clarified and expanded item creation rules

Added full descriptions of key feats. New Craft subskills are in
progress. Also revised Craft mechanics for nonmagical items,
significantly improving crafting times for skilled crafters. A 10th
level PC smith with legendary skill can now make full plate in about two
weeks - or a longsword in about an hour!
Reorganized magic item descriptions

Organization is now "Apparel", "Implements", "Tools".