Use AVR-Crypto lib with ASM imlplementation of AES instead of the C implementation. This speeds up encoding and decoding times by a factor of at least 50 (incl. loading the AES key). This is especially relevant for low speed devices (1 MHz) like the EnvSensor to reduce power consumption, because encoding a 16 byte block now takes <20ms instead of ~750ms. The Makefiles are changed so that all temporary files are stored under the Build path of the device.