Fix 15 snoop (#752)

* fixing hf 15: implement hf 15 snoop
* rename hf 15 record to hf 15 snoop
* speedup sampling / decoding:
*   new FPGA mode FPGA_HF_READER_RX_XCORR_AMPLITUDE implements amplitude(ci, cq) on FPGA
*   inlining the decoders in iso15693.c
*   inlining memcpy/memset in LogTrace()
*   giving up the moving correlator for SOF in Handle15693SamplesFromTag
* decode more of EOF in Handle15693SamplesFromTag()
* some refactoring