Rewrote defs specs.
Rewrote iter specs.
Added keyword sexps to defn specs.
Added keyword sexps to defs specs.
Added keyword sexps to iter specs.
A few more keyword args tweaks.
Regen'd parser.
Updates based on 2.1.2 parser.
Cleaned up new *_op_assign usage.
More parser compatibility cleanup.
Parser no longer emits TO_ARY nodes for a, b = c.
Convert op_asgn operators.
Regen'd parser.