sdk: Move `signers` module into `signer` module

sdk/src/lib.rs

@@ -5,6 +5,8 @@
 // Allows macro expansion of `use ::solana_sdk::*` to work within this crate
 extern crate self as solana_sdk;
 
+#[cfg(feature = "full")]
+pub use signer::signers;
 pub use solana_program::*;
 
 pub mod account;
@@ -41,7 +43,6 @@ pub mod secp256k1_instruction;
 pub mod shred_version;
 pub mod signature;
 pub mod signer;
-pub mod signers;
 pub mod stake_weighted_timestamp;
 pub mod system_transaction;
 pub mod timing;

sdk/src/signer/mod.rs

@@ -13,6 +13,7 @@ use {
 pub mod keypair;
 pub mod null_signer;
 pub mod presigner;
+pub mod signers;
 
 #[derive(Debug, Error, PartialEq)]
 pub enum SignerError {

sdk/src/signer/signers.rs

@@ -4,6 +4,7 @@ use crate::{
     signature::{Signature, Signer, SignerError},
 };
 
+/// Convenience trait for working with mixed collections of `Signer`s
 pub trait Signers {
     fn pubkeys(&self) -> Vec<Pubkey>;
     fn try_pubkeys(&self) -> Result<Vec<Pubkey>, SignerError>;