Shard node

[villanuevawill]

Major WIP in progress. The shard chain is compiling and running end-to-end. Also contains major changes to the beacon chain.
Lots of cleanup needed!

Cleanup Tasks:

• Update to latest spec (pull in current master from sigp)
• Move some chain_spec values into shard_state_types to make for easier ShardSlot, Slot, Epoch, Period conversions
• Refactor the shard state processing functions into its own package
• Clean up errors trickling up for the shard chain (too much duplication from the beacon chain and leftovers).
• Build proper error handling for state processing functions. Particularly, follow the design patterns from block_processing and epoch_processing
• Introduce Shard struct instead of just a u64
• Refactor chain_spec values to be exactly in line with the spec. Add the new configs in as well
• Refactor store and eth2 lmd_ghost directory to operate on Generics. Too much duplication currently
• Refactor some loops into iterators (improve on Rust paradigms)
• Comments / doc comments!!
• Include verification of attestations within the op_pool

Core Functionality

• Plug in Scout to per_shard_block_processing
• Build out the rest of the state processing functions from the spec
• Command line tooling to inject the wasm for the EE and add the block data in realtime
• Add persistence

Harness

• Complete harness logic
• ShardStateBuilder for Genesis block

Efficiency Gains

• Refactor block/state iterators to take advantage of log search in history_accumulator or build a linear cache/vector of historical roots (probably the better option)
• Plug in metrics/prometheus and begin using it to benchmark functions, etc.

Tests

• Builders, builders, builders :)
• Expand beacon state tests to accommodate recent additions
• Tests for shard state processing and other logic in addition to Shard Chain tests

Future

• Harness adds multiple shard chains
• Further logic, transaction types in beacon chain
• Partials/proof for receipts from the shard chain (deltas as well)
• Some basic networking
• RPC interface/functions
• Lots of simulations (relay markets, crosslink clients, etc.)