Connect to bsv node

[calvogenerico]

This PR adds an API implementation to directly connect run-db to a bitcoin node.

A few considerations:

• At the moment this parses entire blocks in memory, which means that is probably not ready for mainnet.
• It subscribes zmq message rawtx.
• It adds zeromq as optional dependecy. I used the optional dependency section because it has system dependencies and is not needed if you use any other api.
• the error handling for rpc is pretty basic.
• I was able to succesfully load testnet in my local env doing this.
• There is no tests for the real implementation of zmq and rpc. Those are basically axios and zeromq packages. I don't believe that those tests add a lot value.

[codecov[bot]]

Codecov Report

Merging #11 (07bcf3d) into master (1f88cc2) will increase coverage by 0.39%. The diff coverage is 93.54%.

@@            Coverage Diff             @@
##           master      #11      +/-   ##
==========================================
+ Coverage   80.98%   81.37%   +0.39%     
==========================================
  Files           8        9       +1     
  Lines         957      988      +31     
==========================================
+ Hits          775      804      +29     
- Misses        182      184       +2     

Impacted Files	Coverage Δ
src/bitcoin-node-connection.js	93.10% <93.10%> (ø)
src/config.js	100.00% <100.00%> (ø)

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[brentongunning]

Great work @hojarasca, and excellent tests. Now we have something available on testnet.