implement creative telescoping

[rwst]

Creative telescoping denotes a set of algorithms for the discovery of identities, i.e., closed forms in terms of holonomic functions (equivalent to finding polynomial recurrences). This allows automatic conjectures (and proof), and so, using older algorithms, Maxima can solve some sums and integrals using Wilf-Zeilberger theory. More general however are Chyzak's algorithm and the work by Koutschan. Already available optionally in Sage is the Ore algebra package that is needed here.

This meta-ticket implements the full toolkit for holonomic functions similar to Koutschan's Mathematica package HolonomicFunctions, see http://koutschan.de.

CC: @kcrisman

Component: symbolics

Issue created by migration from https://trac.sagemath.org/ticket/16636