Make API friendly to block explorers (#702)

* Add validator index to duties response

* Add `get_state` method to beacon chain

* Improve /beacon/validators endpoint

* Add validators/all and validators/active endpoints

* Start refactor of HTTP docs

* Document /beacon/heads endpoint

* Remove some unused API endpoints

* Improve API docs

* Add methods to get all validator duties

* Improve docs

* Remove dead links

* Make tables left-justified

* Add /consensus/vote_count endpoint

* Add /consensus/individual_votes endpoint

* Update formatting

* Tidy

* Add committees endpoint

* Strictly require 0x prefix for serde in BLS

* Update docs to have 0x prefix

* Fix failing tests

* Add unfinished code

* Improve testing, fix bugs

* Tidy, ensure all beacon endpoints smoke tested

* Fix pubkey cache error

* Address comments with docs

eth2/state_processing/src/per_epoch_processing.rs

@@ -1,7 +1,6 @@
 use errors::EpochProcessingError as Error;
 use tree_hash::TreeHash;
 use types::*;
-use validator_statuses::{TotalBalances, ValidatorStatuses};
 
 pub mod apply_rewards;
 pub mod errors;
@@ -13,6 +12,7 @@ pub mod validator_statuses;
 pub use apply_rewards::process_rewards_and_penalties;
 pub use process_slashings::process_slashings;
 pub use registry_updates::process_registry_updates;
+pub use validator_statuses::{TotalBalances, ValidatorStatus, ValidatorStatuses};
 
 /// Performs per-epoch processing on some BeaconState.
 ///