[GSoC 2016] Refactoring of expressions

Hello all!

I spent the last few days working on refactoring the old expressions.rb (in ruby runtime environment) into a revamped CT_Expressions module. This solves the issue of namespaces thus giving flexibility to names being used in the Curry programs. The entire module is divided into 4 files - expression class definitions, expression printing, expression equality and expression utilities. We tested this new module on all the existing test cases.

After this refactoring I moved ahead to implement the equality operation algorithm in CT_External which has also been completed now.

I am now working on the Prelude compare operation based on this algorithm.