AccountantSkel -> Tpu

The terms Stub and Skel come from OMG IDL and only made sense while
the Stub was acting as an RPC client for the the Accountant object.
Nowadays, the Stub interface looks nothing like the Accountant and
meanwhile we've recognized the multithreaded implementation is more
reminiscent of a pipelined CPU. Thus, we finally bite the bullet and
rename our modules.

AccountantSkel -> Tpu
AccountantStub -> ThinClient

Up next will be moving much of the TPU code into separate modules,
each representing a stage of the pipeline. The interface of each
will follow the precedent set by the Historian object.

src/bin/testnode.rs

@@ -7,7 +7,7 @@ extern crate solana;
 use getopts::Options;
 use isatty::stdin_isatty;
 use solana::accountant::Accountant;
-use solana::accountant_skel::AccountantSkel;
+use solana::tpu::Tpu;
 use solana::crdt::ReplicatedData;
 use solana::entry::Entry;
 use solana::event::Event;
@@ -119,7 +119,7 @@ fn main() {
     let (input, event_receiver) = sync_channel(10_000);
     let historian = Historian::new(event_receiver, &last_id, Some(1000));
     let exit = Arc::new(AtomicBool::new(false));
-    let skel = Arc::new(AccountantSkel::new(acc, input, historian));
+    let tpu = Arc::new(Tpu::new(acc, input, historian));
     let serve_sock = UdpSocket::bind(&serve_addr).unwrap();
     let gossip_sock = UdpSocket::bind(&gossip_addr).unwrap();
     let replicate_sock = UdpSocket::bind(&replicate_addr).unwrap();
@@ -132,8 +132,8 @@ fn main() {
         serve_sock.local_addr().unwrap(),
     );
     eprintln!("starting server...");
-    let threads = AccountantSkel::serve(
-        &skel,
+    let threads = Tpu::serve(
+        &tpu,
         d,
         serve_sock,
         skinny_sock,