Convert An AD or Base Type to String

Syntax
s = to_string(value) .

The argument value has prototype       const AD<Base>& value      const Base&     value  where Base is a type that supports the base_to_string type requirement.
The return value has prototype       std::string s  and contains a representation of the specified value . If value is an AD type, the result has the same precision as for the Base type.
The file to_string.cpp includes an example and test of to_string with AD types. It returns true if it succeeds and false otherwise.