Release: v0.0.4

• fix: -> on difference directory
• fix: expression - and / is wrong because stack popping error.
• fix: regular expression escape
• fix: declare variable which isn't following top-down law
• fix: ### multiline comment working incorrectly ###
• add: support data<-{other_variable}+5 in header
• add: error Unexpected declaration in header.
• add: error Variable name must not start with number.
• add: error unexpected indentation
• remove: error Header must have no indent. (replace by unexpected indentation)