Add two Poseidon Filecoin variant multihashes

Reserving the 0xb400 range for Poseidon variants, allowing FIL to
iterate on the `fcX` extension of the name where they stay with
BLS12-381 and arity=2. High security variant is for extra circuits
that are usable in case new attacks arise from the standard variant.

Ref: #161
Ref: https://eprint.iacr.org/2019/458.pdf

table.csv

@@ -430,6 +430,8 @@ skein1024-1000,                 multihash,      0xb3dd,
 skein1024-1008,                 multihash,      0xb3de,
 skein1024-1016,                 multihash,      0xb3df,
 skein1024-1024,                 multihash,      0xb3e0,
+poseidon-bls12_381-a2-fc1,      multihash,      0xb401,         Poseidon using BLS12-381 and arity of 2 with Filecoin parameters
+poseidon-bls12_381-a2-fc1-sc,   multihash,      0xb402,         Poseidon using BLS12-381 and arity of 2 with Filecoin parameters - high-security variant
 holochain-adr-v0,               holochain,      0x807124,       Holochain v0 address    + 8 R-S (63 x Base-32)
 holochain-adr-v1,               holochain,      0x817124,       Holochain v1 address    + 8 R-S (63 x Base-32)
 holochain-key-v0,               holochain,      0x947124,       Holochain v0 public key + 8 R-S (63 x Base-32)