Added new guessing functionality

Added new guessing functionality

Added three new methods to toDiffAlgebraic.py
	- A method that, if y(x) = exp(int(u(x))), computes the differential polynomials
	U_n(u) such that y^(n)(x) = y(x)U_n(u). (Exponential_polynomials)
	- A method that, given an homogeneous differentially algebraic equation suppose
	that the solution is of the form y(x) = exp(int(u(x))) and computes a
	differentially algebraic equation for u(x) which will have less order than y(x).
	(simplify_homogeneous)
	- A method that, given an homogeneous differentially algebraic equation use the
	method simplify_homogeneous and in case that a linear equation is achieved, then
	a Dn-finite function is returned as an iteration of exponential functions
	(guess_homogeenous_DNfinite).