Add watcher to auto-compile Solidity Files

[João Augusto Perin]

Hello guys!

First off I wanna thank you for the awesome, although concise library!

But this section/feature on Readme, got me thinking, maybe could we automate this?

To compile the test solidity contracts after making a change run this command:

$ solc --abi --bin --overwrite -o test/examples/build test/examples/contracts/*.sol

And such, I did as a MVP, a simple implementation, that you can check out here. I did some changes, implemented better automations, and error treatments. But unfortunately I couldn't create a branch here 😢 .

So Here's my request, can we got my PR here, and such we can get this working? I already integrated with the library, and tested in a sample Phoenix Framework Project: