Misc API cleanup

[marktsuchida]

• Functions returning arrays of borrowed objects (OSc_GetAllDevices(), OSc_Device_GetSettings()) should not return borrowed array. Instead they should copy into caller-provided array (or introduce a PtrArray type).
• Functions returning strings should standardized to using fixed-size (OSc_MAX_STR_SIZE) buffers: OSc_Device_GetName() and OSc_Device_GetDisplayName().
• Avoid losing information: separate OSc_Device_GetDisplayName() into two functions, for model name and device name.
• OSc_SetDeviceModuleSearchPaths() parameter type should be const char *const *.
• Error-related functions that write to string buffer should return would-be-written string length rather than void.
• Settings functions returning arrays of numbers should avoid returning internal pointer (whose lifetime is hard to specify) and copy to caller-provided buffer (or introduce NumArray type).