Number types: Add double ceil(NT)

[afabri]

Summary of Changes

Add function double ceil(const NT&).

Release Management

• Affected package(s): Algebraic_foundations, Number_types
• Feature/Small Feature (if any):
• Link to compiled documentation (obligatory for small feature) wrong link name to be changed
• License and copyright ownership: unchanged

[afabri]

I commented out several test cases in Number_types/test/utilities.cpp, where I do not understand why they do not compile.
I did not address CORE::Expr. Also I have no idea what to put for Sqrt_extension.

[mglisse]

The standard function std::ceil returns long double when passed a long double and essentially tries to return the same type as its input. It is only for integers that they decided to force the return type to double, probably for consistency with the historical C behavior.
If you want a function that always returns a double, I think using a different name might be clearer.