Split tokio-threadpool lib.rs into files (#233)

* Builder -> src/builder.rs
* Callback -> src/callback.rs
* Config -> src/config.rs
* Futures2Wake -> src/futures2_wake.rs
* Inner -> src/inner.rs
* Notifier-> src/notifier.rs
* Sender -> src/sender.rs
* Shutdown -> src/shutdown.rs
* ShutdownTask -> src/shutdown_task.rs
* SleepStack -> src/sleep_stack.rs
* State -> src/state.rs
* ThreadPool -> src/thread_pool.rs
* Worker -> src/worker.rs
* WorkerEntry -> src/worker_entry.rs
* WorkerState -> src/worker_state.rs

tokio-threadpool/src/config.rs

@@ -0,0 +1,18 @@
+use callback::Callback;
+
+use std::time::Duration;
+
+/// Thread pool specific configuration values
+#[derive(Debug, Clone)]
+pub(crate) struct Config {
+    pub keep_alive: Option<Duration>,
+    // Used to configure a worker thread
+    pub name_prefix: Option<String>,
+    pub stack_size: Option<usize>,
+    pub around_worker: Option<Callback>,
+}
+
+/// Max number of workers that can be part of a pool. This is the most that can
+/// fit in the scheduler state. Note, that this is the max number of **active**
+/// threads. There can be more standby threads.
+pub(crate) const MAX_WORKERS: usize = 1 << 15;