Submodule secp256k1 instead of copying files

[mecampbellsoup]

Inpsired by: https://github.com/ACINQ/bitcoin-lib/pull/17/files

[mecampbellsoup]

@Christewart how to trigger the build checks e.g. Coveralls?

[mecampbellsoup]

[info] ! EscrowWithTimeoutScriptSigSpec.serialization symmetry: Exception raised on property evaluation.
[info] > Exception: java.lang.UnsatisfiedLinkError: org.bitcoin.NativeSecp256k1.secp256k1_ec_pubkey_decompress(Ljava/nio/ByteBuffer;JI)[[B

[info] ! P2PKScriptPubKeySpec.Serialization symmetry: Exception raised on property evaluation.
[info] > Exception: java.lang.UnsatisfiedLinkError: org.bitcoin.NativeSecp256k1.secp256k1_ec_pubkey_decompress(Ljava/nio/ByteBuffer;JI)[[B

[info] ! ECDigitalSignatureSpec.must create and verify a digital signature: Exception raised on property evaluation.
[info] > ARG_0: DoubleSha256DigestImpl(10e5a184d30854be4d8dd3a246dc78c622746bd55d3cacda4c6f97ff7b05f502)
[info] > ARG_1: ECPrivateKey(2e59c250b84a4419a62273a00c6eada91f7dcdd245d16135b685946f5a87dbff,true)
[info] > Exception: java.lang.UnsatisfiedLinkError: org.bitcoin.NativeSecp256k1.secp256k1_ec_pubkey_decompress(Ljava/nio/ByteBuffer;JI)[[B

Seeing a lot of test failures like ☝️ which leads me to think the secp256k1 submodule isn't... discoverable/linked?

[Christewart]

I'm not sure why travis isn't being kicked off. But yes it looks like the secp256k1 module isn't being found. Does the relative path change when incorporating a submodule? I.e. is it not bitcoin-s-core/secp256k1 anymore?

[coveralls]

Coverage increased (+0.02%) to 90.29% when pulling 9f91b3b on mecampbellsoup:submodule-secp256k1 into 51d0ec7 on bitcoin-s:master.

[mecampbellsoup]

@Christewart hey, we're green again! This is a no-op change so hopefully you're OK merging 😄

[Christewart]

Merged. Congrats @mecampbellsoup . We will need to update this whenever bitcoin-core/secp256k1#508 gets merged