Dynamically linked libraries

[RaoulSchaffranek]

Dynamically linked libraries cause a crash during deployment time.

We should:

1. Create test cases
2. Update our documentation with a working example for dynamically linked libraries.
3. Improve the error messages

[RaoulSchaffranek]

This turned out to be slightly more involved than anticipated. It's not sufficient to just deploy and link the libraries before deploying the main contract. We must also change various places touching the sourcemaps.

This PR to pyevmasm should help us with the latter.

• Add instruction offsets to simplify source mapping crytic/pyevmasm#66