Changed Integer to Long_Float and bug fixes

Changed Integer in the operator functions to Long_Float so that decimal
numbers can be used. Had to bring in
Ada.Numerics.Generic_Elementary_Functions so that we had a power
function. Also fixed some bugs, namely function definitions not matching
specification and evaluateTree(extree.right) to return
evaluateTree(extree.root.right)
added expression printing functions

added printTreeInFix and printTreePreFix