Add IMap Repo

Add SmartCookie project.

Update README.md

Compared to HalfSipHash sibling:
1. Changed intermediate variables into 64 bit
2. Change shift to match 64-bit specs. Use two separate in_hash to output 32+32=64 bits
3. Only does one round per pipeline pass.

Update README.md

[P4RTT] Change from 1-stage to 2-stage

Merged Vladimir's suggested cleanups.

Important hash-related optimizations and cleanups:
   1. Replaced hash-based 8-, 16- and 24-bit circular shifts (rotations) with the PHV ALU-based ones
   2. Replaced explicit Hash() extern instantiations and usage with `@in_hash` annotation (available in SDE-9.6.0 and later)

   1. Replaced hash-based 8-, 16- and 24-bit circular shifts (rotations) with the PHV ALU-based ones
   2. Replaced explicit Hash() extern instantiations and usage with `@in_hash` annotation (available in SDE-9.6.0 and later)

Updated README.md with SP-PIFO (NSDI'20)

Add links to ATP and ATP-SwitchML