Advanced execution modes

[AlanVerbner]

Description

web3-repl should allow two different execution modes

1. Exec single command and exit in order to provide users a way to get some simple info and exit

> web3-repl -p http://localhost:8545 -e "web3.eth.blockNumber

2. Allow users to execute a file with a predefined script to allow them to run several predefined

> web3-repl -p http://localhost:8545 -f myWeb3BasedScript.json