Parse defklassparse
Fix Rakefile for peg
normalize :defclass
infer class object
rename 'receiver' to 'callee'
Parse method invocation
fix: A should be a Class
Raise error for misplaced `class'
Infer A.new
rename `defklass` to `defclass`
Parse method defs inside class def
Use UNIT_EXPR
fix Subst#merge omitting self from result

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Fix failing test

Removed assetion of `subst`
Parse defmethod