Avoid memory leakage for FPGA track, close #1372

add dwconv compute function in FPGA and update some other files fixed#1368

modify ios interface

add fpga dwconv and reshape op and refactor code of fpga conv and dec… fixed#1366

reduce memory during initialization for FPGA track close #1364

suit raspberry compile on gcc fixed #1361

Refactor predict api, optimize softmax, add top_k and cast operators