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/utils/bls/src/secret_key.rs

@@ -5,7 +5,7 @@ use hex::encode as hex_encode;
 use milagro_bls::SecretKey as RawSecretKey;
 use serde::de::{Deserialize, Deserializer};
 use serde::ser::{Serialize, Serializer};
-use serde_hex::HexVisitor;
+use serde_hex::PrefixedHexVisitor;
 use ssz::{ssz_encode, Decode, DecodeError, Encode};
 
 /// A single BLS signature.
@@ -65,7 +65,7 @@ impl<'de> Deserialize<'de> for SecretKey {
     where
         D: Deserializer<'de>,
     {
-        let bytes = deserializer.deserialize_str(HexVisitor)?;
+        let bytes = deserializer.deserialize_str(PrefixedHexVisitor)?;
         let secret_key = SecretKey::from_ssz_bytes(&bytes[..])
             .map_err(|e| serde::de::Error::custom(format!("invalid ssz ({:?})", e)))?;
         Ok(secret_key)