rashmi v / Mbed 2 deprecated SS_SensePOC2P0_12Dec2017_USERPID

created separate function for hex to char

Dependencies:   SDFileSystem ds3231 eeprom_Nikita mbed testUniGraphic_150217

Fork of SS_SensePOC2P0_11Dec2017_USERPID by rashmi v

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sdcard.h/shortlog@907f8ce0025e: not found in manifest