De-duplicate and correct view-item / use rules.
Re-factor struct_expr.
Enable all-errors warning mode on bison.
Fix useless precedences and fix the various path forms (documenting context).
Fix empty rules and remove useless rules. Builds with error=all now.
Add item_type.
Add item_trait.
Add item_impl.
Flesh out pat, add paths to exprs.
Flesh out ty, add path_expr permitting leading MOD_SEP.
Merge pull request #8 from ptgreen/misc-lalr-enhancements

Misc LALR enhancements