Fix clippy warnings (#813)

* Clippy account manager

* Clippy account_manager

* Clippy beacon_node/beacon_chain

* Clippy beacon_node/client

* Clippy beacon_node/eth1

* Clippy beacon_node/eth2-libp2p

* Clippy beacon_node/genesis

* Clippy beacon_node/network

* Clippy beacon_node/rest_api

* Clippy beacon_node/src

* Clippy beacon_node/store

* Clippy eth2/lmd_ghost

* Clippy eth2/operation_pool

* Clippy eth2/state_processing

* Clippy eth2/types

* Clippy eth2/utils/bls

* Clippy eth2/utils/cahced_tree_hash

* Clippy eth2/utils/deposit_contract

* Clippy eth2/utils/eth2_interop_keypairs

* Clippy eth2/utils/eth2_testnet_config

* Clippy eth2/utils/lighthouse_metrics

* Clippy eth2/utils/ssz

* Clippy eth2/utils/ssz_types

* Clippy eth2/utils/tree_hash_derive

* Clippy lcli

* Clippy tests/beacon_chain_sim

* Clippy validator_client

* Cargo fmt

eth2/utils/ssz/src/decode.rs

@@ -99,7 +99,7 @@ impl<'a> SszDecoderBuilder<'a> {
             let previous_offset = self
                 .offsets
                 .last()
-                .and_then(|o| Some(o.offset))
+                .map(|o| o.offset)
                 .unwrap_or_else(|| BYTES_PER_LENGTH_OFFSET);
 
             if (previous_offset > offset) || (offset > self.bytes.len()) {
@@ -179,7 +179,7 @@ impl<'a> SszDecoderBuilder<'a> {
 ///     b: Vec<u16>,
 /// }
 ///
-/// fn main() {
+/// fn ssz_decoding_example() {
 ///     let foo = Foo {
 ///         a: 42,
 ///         b: vec![1, 3, 3, 7]

eth2/utils/ssz/src/decode/impls.rs

@@ -207,9 +207,10 @@ impl Decode for bool {
             match bytes[0] {
                 0b0000_0000 => Ok(false),
                 0b0000_0001 => Ok(true),
-                _ => Err(DecodeError::BytesInvalid(
-                    format!("Out-of-range for boolean: {}", bytes[0]).to_string(),
-                )),
+                _ => Err(DecodeError::BytesInvalid(format!(
+                    "Out-of-range for boolean: {}",
+                    bytes[0]
+                ))),
             }
         }
     }

eth2/utils/ssz/src/encode.rs

@@ -64,7 +64,7 @@ pub trait Encode {
 ///     b: Vec<u16>,
 /// }
 ///
-/// fn main() {
+/// fn ssz_encode_example() {
 ///     let foo = Foo {
 ///         a: 42,
 ///         b: vec![1, 3, 3, 7]

eth2/utils/ssz/src/lib.rs

@@ -17,7 +17,7 @@
 //!     b: Vec<u16>,
 //! }
 //!
-//! fn main() {
+//! fn ssz_encode_decode_example() {
 //!     let foo = Foo {
 //!         a: 42,
 //!         b: vec![1, 3, 3, 7]