Clean up rules for ty.
Allow 0-element delimited token trees.
Allow '.' as token in token tree.
Clean up duplicate str / lit_str mess.
Fix ItemMod.
Sink ItemFoo constructors into sub-rules.
Remove unary ~, add unary &.
Allow nonblock_prefix_expr in expr position, permitting unary exprs.
Alignment cleanup.
Add 'self' as special case ExprPath.
Flesh out rules for traits, impls, methods.