Now we calculate the round changes and store them in generate_block.

Progress:
- When an account adds/removes stake, we now update votes for its
approved producers
- Name map<AccountName, AccountName> as RoundChanges, and define
operator- such that RoundChanges = ProducerRound - ProducerRound

Test the vote updates, making sure that producer votes are updated when
an account adds stake

TODO: Calculate the producer round changes in generate_block and add to
block header

From where I'm standing, #35 is just due to the outdated genesis.json
and docs. Looks fixed to me.

Fix wasm_interface bug and other assorted changes

Add llvm dependency to Docker

An account can now approve a producer, and that producer's votes are
increased appropriately. The account can remove approval, and the votes
are decreased appropriately. Additionally, the producer is added/removed
to the account's approved producers list as desired.

TODO: A producer with more votes than the rest is still never rotated in

Calculating the new producer schedule based on votes is now implemented;
however, the voting itself is not. :D But the code builds, and the tests
pass. It's good progress, it's been a good day.

Note that "the tests pass" means little at this stage, since I haven't
written any new tests to exercise the new code. In other words, NEEDS
TESTING!

- Rename config::ProducerCount -> config::BlocksPerRound
- Add new config::VotedProducersPerRound = 20
- Split up staked_balance_objects.hpp moving ProducerVotesObject to
producer_objects.hpp

Add producer schedule changes to block_header, so light clients can see
the round changes by just watching block headers.

Implement changing the producer schedule at round changes, first checking
that the schedule changes in the block_header are correct, then applying
them.

TODO: Actually calculating the new round (right not it never changes)

Wire protocol specs say never to put an id_type on the wire, but
block_header contained the id_type for the producer which created it.
Fix this by using the AccountName of the producer's owner instead.

The producer-median-voted blockchain configuration parameters are now
updated when the round changes. The previously expected-failing test
case for this now passes

This new interface allows the chain_controller to request a fresh round
of producers and request the producers' median voted blockchain
configuration.

Net yet complete, but integrated sufficiently to get the tests to pass.

And rename it to chain_initializer_interface