New predicate Meaning#missing?, differnt from has?

has?(part) <-> part is not nil
missing?(part) <-> part is a variable (number)
Player#lookup: start with most missing meaning
Meaning#matches_part? only check for other.missing if has part
Don't continue Player#lookup if got nil for a word
Breakpoint in test.rb
Fix Grammar#embed! to cast index
test.rb output result word
Player#lookup: single return point
Meaning#full? checks missing parts only