Crank: Limit header file exports to those files which must be exported.

[pyjarrett]

Purpose

Reduce the number of header files exported to only those required for library usage.

Method

• Include a special empty macros to identify these headers, which gets checked against usage of CN_API to detect headers which should be exported, but are not.

For public header files which should be exported:

#define CN_EXPORT_HEADER

For header files which should not be exported:

#define CN_PRIVATE_HEADER

crank should issue an error during export and abort if CN_API exists in a private header.

• Modify the export command in crank to only copy public headers to the exported library location.