A lot of work has been done to improve the fees situation! More fields are handled that have an impact on fees computation. For example, the presence of collateral in the Tx when there are scripts.
This PR also adds tests, a dedicated Error type, and many code improvements for processing intents.

Things still left to do:

• check minAda for auto generated outputs (assets sent at other addresses and the change)
• correct implementation of scriptDataHash: prepare the whole thing but leave the final hashing for a follow up PR
• define the ports to evaluate scripts costs

MinAda is now automatically checked and adjusted for everything! So we have only these two left:

• correct implementation of scriptDataHash: prepare the whole thing but leave the final hashing for a follow up PR
• define the ports to evaluate scripts costs

Ok, this is almost ready. As previously said, there are only two things left:

• correct script data hash, that will need Add BLAKE2-b #39
• script costs, that will need Making an elm-cardano binary #41

So let’s merge this, work on those two issues/PRs, then we can go back to finish Tx Building :)