add a function for the derivative of ceil and floor

[burcin]

We should define a new symbolic function for the derivative of ceil or floor.

In Maple:

> diff(floor(x),x);
                                  floor(1, x)
> diff(floor(x),x,x);
                                  floor(1, x)
> diff(ceil(x),x,x); 
                                  floor(1, x)
> eval(diff(ceil(x),x,x),x=1.5);
                                       0
> eval(diff(ceil(x),x,x),x=0);  
Error, (in floor) floor is not differentiable at integers

CC: @sagetrac-ktkohl @rwst @kcrisman @pelegm

Component: symbolics

Keywords: sd35.5

Author: Karen Kohl

Branch/Commit: u/ktkohl/add_a_function_for_the_derivative_of_ceil_and_floor @ 8013b9f

Issue created by migration from https://trac.sagemath.org/ticket/9874

[sagetrac-ktkohl]

Changed keywords from none to sd35.5

[sagetrac-ktkohl]

Author: ktkohl