Rename PublicKey type to Pubkey

Recognize pubkey as a noun meaning the public key of a keypair.

src/request.rs

@@ -1,12 +1,12 @@
 //! The `request` module defines the messages for the thin client.
 
 use hash::Hash;
-use signature::{PublicKey, Signature};
+use signature::{Pubkey, Signature};
 
 #[cfg_attr(feature = "cargo-clippy", allow(large_enum_variant))]
 #[derive(Serialize, Deserialize, Debug, Clone, Copy)]
 pub enum Request {
-    GetBalance { key: PublicKey },
+    GetBalance { key: Pubkey },
     GetLastId,
     GetTransactionCount,
     GetSignature { signature: Signature },
@@ -21,7 +21,7 @@ impl Request {
 
 #[derive(Serialize, Deserialize, Debug)]
 pub enum Response {
-    Balance { key: PublicKey, val: i64 },
+    Balance { key: Pubkey, val: i64 },
     LastId { id: Hash },
     TransactionCount { transaction_count: u64 },
     SignatureStatus { signature_status: bool },