Add initial support for Cosmos.

[tritao]

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As the title says, adds support for Cosmos-based networks.

Tested against the terra.js SDK.

[farukterzioglu]

Awesome, I will check as soon as possible.

[farukterzioglu]

Does Cosmos have any implementation other than Secp256k1? If not we can name it as just CosmosHDWallet not CosmosHDWalletSecp256k1. All of the wallets follow this naming, except Tezos which has both Secp256k1 and Ed25519 (not in this project though) implementation. Thats why it is called as TezosHDWalletSecp256k1

If cosmos doesn't have Ed25519 implemenration in use, you can name it to CosmosHDWallet

[tritao]

Does Cosmos have any implementation other than Secp256k1? If not we can name it as just CosmosHDWallet not CosmosHDWalletSecp256k1. All of the wallets follow this naming, except Tezos which has both Secp256k1 and Ed25519 (not in this project though) implementation. Thats why it is called as TezosHDWalletSecp256k1

If cosmos doesn't have Ed25519 implemenration in use, you can name it to CosmosHDWallet

Sounds good, I will update the PR with the rename.

[farukterzioglu]

@tritao Could you get the latest changes from master and do the mentioned changes above, so I can merge this.