ndarray function source code.

• Each file contains a set of related ndarray functions. The file name matches the ndarray function name suffix for output ndarray dtype.
• The implemented functions which perform conversions are not exhaustive and that is intentional. Namely, functions which would perform "unsafe" callback return value conversions are not included (e.g., converting double to int32). If users want to perform "unsafe" conversions, that should be a conscious decision. All the machinery (e.g., macros, typedefs, etc) is available for implementing ndarray functions which perform "unsafe" conversions, but we should not make this overly easy or be proactive in promoting "unsafe" conversion use.