Add spectests for all types and clauses and properties that have not been equipped with them. The spectest is now pretty complete and covers most of the specification document. Some clause attributes and advanced features (like expresssion and function) have not been covered though.
INCOMPATIBLE CHANGES
Rename obj properties: 'methods' -> 'meths', 'attributes' -> 'attrs'. This is to be consistent with design principle 'abbreviate when common abbreviation is present and won't introduce ambiguity'.
REMOVED FEATURES
Remove hash 'req_keys_re', which doesn't make any sense.