Spu

- [Bugfix] Fix SEMI2K division wrong answer

20220324

- [Improvement] Lift Convolution limitations.
- [Improvement] Optimize maximum/minimum speed, with MPC B2A single bit conversion.
- [Experimental] Div is calculated with direct goldschmdit method instead of
multiplication of dividend and divisor reciprocal.
- [API] change RuntimeConfig.enable_op_time_profile to enable_pphlo_profile.
- [API] change RuntimeConfig.fxp_reciprocal_goldschmdit_iters to fxp_div_goldschmdit_iters.

20220308

- [Feature] add silent ot support for various ot scenarios (chosen/correlated/random
messages, chosen/correlated/random choices, 1o2/1oN)
- [Feature] add non-linear computation protocols based on silent ot (comparison,
truncation, b2a, triple, randbit, etc)
- [Feature] add a 2PC protocol: Cheetah
- [Improvement] concatenate is a lot faster
- [API] add RuntimeConfig.enable_op_time_profile to ask SPU to collect timing profiling data
- [Bugfix] fixed pphlo.ConstOp may lose signed bit after encoding

20220303

- [API] merge (config.proto, executable.proto, types.proto) into single spu.proto.
- [API] change RuntimeConfig.enable_protocol_trace to enable_action_trace.
- [API] change RuntimeConfig.fxp_recirptocal_goldschmdit_iters to fxp_reciprocal_goldschmdit_iters.
- [API] add RuntimeConfig.reveal_secret_condition to allow reveal secret control flow condition.
- [Bugfix] Fixed SEGV when reconstruct from an ABY3 scalar secret
- [Feature] Left/right shift now properly supports non-scalar inputs

20220217

20220211

- [Bugfix] Fix exception when kkrt psi input is too small

20220210