update .gitignore
remove old ModernWalker grammar
change variable to variableDeclaration
change cstat to statement
require semicolon after expression and assignment statements
change forStat to forStatement
change old cstat to statement
change assignStat to assignStatement
change expr to expression
change condExpr to comparisonExpression
change logicOperator to comparisonOperator
change aexpr to additionExpression
change old variable to variableDeclaration
change mexpr to multiplicationExpression
change atom to literal
regenerate parser and lexer code