Signature package could use JSON instead of regex

[ansermino]

I believe that the version of subkey presently used supports JSON formatting which would likely be more reliable than regex and easier to upgrade.

Here's an example:

d@P51:~$ subkey --output=json inspect //Alice
{
  "accountId": "0xd43593c715fdd31c61141abd04a99fd6822c8558854ccde39a5684e7a56da27d",
  "publicKey": "0xd43593c715fdd31c61141abd04a99fd6822c8558854ccde39a5684e7a56da27d",
  "secretKeyUri": "//Alice",
  "secretSeed": "0xe5be9a5092b81bca64be81d212e7f2f9eba183bb7a90954f7b76361f6edb5c0a",
  "ss58Address": "5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY"
}

[mikiquantum]

Fixed by #98