replace 'struct array2d' with 'class array2d' for consistency
replace 'struct array2d' with 'class array2d' for consistency

Reported by Bart Kevelham

victordion/cusp-library,tectronics/cusp-library,gshashidhar125/cusp-library,baiyunping333/cusp-library,vkirangoud/cusp-library,tectronics/cusp-library,victordion/cusp-library,tectronics/cusp-library,vkirangoud/cusp-library,tectronics/cusp-library,gshashidhar125/cusp-library,gshashidhar125/cusp-library,vkirangoud/cusp-library,victordion/cusp-library,baiyunping333/cusp-library,vkirangoud/cusp-library,baiyunping333/cusp-library,baiyunping333/cusp-library,gshashidhar125/cusp-library,victordion/cusp-library