v0.5.0b0

[Feature] Add DGK cryptosystem
[Feature] Add Damgard-Jurik cryptosystem
[Feature] Add a new paillier implementation based on ClustarFPGA hardware from Clustar Technology
[Feature] Add an experimental implementation of GPU-based paillier cryptosystem
[Feature] Add ic-paillier that meets CAICT interconnection standards
[Optimize] Optimize vectorized spi in mat mul
[Add] Add test case Mul in NpBenchmarks
[Add] New api: Create HeKit by pre-generated pk ans sk