Add logging to all requests

[pedrobranco]

This PR adds logging to all requests made with bitcoin-core, using as logger the seegno/debugnyan module.

Since there is sensitive data in the following methods calls:

• dumpprivkey
• encryptwallet
• importprivkey
• signmessagewithprivkey
• signrawtransaction
• walletpassphrase

by default we are obfuscating all sensitive data with the string ******.

[pedrobranco]

You mention an obfuscation option in the PR, but the code has none.

I'd rather leave the obfuscating only for the default logger. I'll leave the obfuscation both for default and custom logging.

[pedrobranco]

This PR now depends on #21.