Schnorr support

[omershlo]

No description provided.

[gbenattar]

As discussed, this branch is ready for merging with master. @omershlo can you please provide a very descriptive bullet list with everything that is included? I will squash and merge.

[omershlo]

@gbenattar sure :

• Schnorr support: The code now supports both 2 party ecdsa and 2 party schnorr based on secp256k1 elliptic curve
• As a result of the previous bullet some design changes were introduced. most notably HD (get child) functionality and rotate functionality became traits and implemented per dsa
• The common parts of those become common functions
• other than that this branch was updated mainly to support changes in ecdsa, schnorr and curv repos. The one worth mentioning is a change to expose full structs publicly for ser/des

[omershlo]

the latest commit is a minor change in the interface of ecdsa signing to support concurrent running. the change reflects in party two ephemeral second message such that instead of argument of dlog_proof the argument is the entire first message from party one