updated to not use deprecated prog_–types

“The usage of the __progmem__ attribute on a type is not supported in GCC. However, the use of the __progmem__ attribute on a variable declaration is supported, and this is now the recommended usage.”

http://www.atmel.no/webdoc/AVRLibcReferenceManual/group__avr__pgmspace_1ga7d4701843a2019e3ef5a9866dc7586ed.html