add command line option to specify the truffle config file to be used

[nphsu]

This is an enhancement request to add a command-line option to specify the truffle config file to be used on the compilation.

I would like to add like the below in the main function.

  let rootIndex = args.indexOf("--root");

[Example]

truffle-flattener contracts/XXX.sol --output build/contracts/FlattenerXXX.sol --dir ./subdir

/rootdir
    |--subdir
    |       |--/contracts
    |       |--/build
    |       |--truffle-config.js
    |--/nodemodules
    |--package.json

[Related]
trufflesuite/truffle#1879

[alcuadrado]

Closing to clean up the repository. If this problem persists, please open a new issue with a clear explanation.