web3-function: implementation of EthProviderInterface

Implements the functions needed to interface the smart contract functions and events with the web3js API.

One should wonder why using web3-eth-contract library encapsulated in smart contract and use web3 encapsulated library in this lib !
First, it is because it was needed to have smart contract code and usage independent of how to reach the blockchain (hexagonal architecture), and Second, because the sending of a transaction to the blockchain requires signature, sometime external, balance control, possible retry, waiting transaction completion ...

Also, this implementation is for the moment relatively trivial, and is firstly built to test smart contracts with a mocha framework using ganache-core as web3 provider.

Usage:
``sh
npm i --save @saturn-chain/web3-function
`
Includes typescript types declaration

Documentation

`typescript
import { Web3FunctionProvider } from "web3-functions";
import Ganache from "ganache-core";

const intf = new Web3FunctionProvider(
// a web3 provider instance or a we3 instance
Ganache.provider() as any,
// an async function receiving a list of available address to select the desired one
list=>Promise.resolve(list[0])
);
``