Standardize folder structure of c, c++, ROS and Arduino - c ver in progress

c/src/dynamixel_sdk/group_sync_read.c

c/src/dynamixel_sdk/group_sync_write.c

c/src/dynamixel_sdk/packet_handler.c

c/src/dynamixel_sdk/port_handler.c

c/src/dynamixel_sdk/port_handler_linux.c

c/src/dynamixel_sdk/port_handler_windows.c

c/src/dynamixel_sdk/protocol1_packet_handler.c

c/src/dynamixel_sdk/protocol2_packet_handler.c