Added Bare Skeleton
 Changes to be committed:
	new file:   src/function/expression.rb
	new file:   src/function/function.rb
	new file:   src/function/operator/binaryoperator/additionoperator.rb
	new file:   src/function/operator/binaryoperator/binaryoperator.rb
	new file:   src/function/operator/operator.rb
	new file:   src/function/operator/unaryoperator/negationoperator.rb
	new file:   src/function/operator/unaryoperator/unaryoperator.rb
	new file:   src/function/value/decimalnumber.rb
	new file:   src/function/value/value.rb
	new file:   src/function/variable/variable.rb