Migrate source files into src/ directory

This change moves source files into a src/ directory,
and puts object files into an obj/ directory. The Makefile
and xcode project are updated accordingly.

Fixes #1866

src/iothread.h

@@ -0,0 +1,55 @@
+/** \file iothread.h
+    Handles IO that may hang.
+*/
+
+#ifndef FISH_IOTHREAD_H
+#define FISH_IOTHREAD_H
+
+/**
+ Runs a command on a thread.
+
+ \param handler The function to execute on a background thread. Accepts an arbitrary context pointer, and returns an int, which is passed to the completionCallback.
+ \param completionCallback The function to execute on the main thread once the background thread is complete. Accepts an int (the return value of handler) and the context.
+ \param context A arbitary context pointer to pass to the handler and completion callback.
+ \return A sequence number, currently not very useful.
+*/
+int iothread_perform_base(int (*handler)(void *), void (*completionCallback)(void *, int), void *context);
+
+/**
+  Gets the fd on which to listen for completion callbacks.
+
+  \return A file descriptor on which to listen for completion callbacks.
+*/
+int iothread_port(void);
+
+/** Services one iothread competion callback. */
+void iothread_service_completion(void);
+
+/** Waits for all iothreads to terminate. */
+void iothread_drain_all(void);
+
+/** Performs a function on the main thread, blocking until it completes */
+int iothread_perform_on_main_base(int (*handler)(void *), void *context);
+
+/** Helper templates */
+template<typename T>
+int iothread_perform(int (*handler)(T *), void (*completionCallback)(T *, int), T *context)
+{
+    return iothread_perform_base((int (*)(void *))handler, (void (*)(void *, int))completionCallback, static_cast<void *>(context));
+}
+
+/* Variant that takes no completion callback */
+template<typename T>
+int iothread_perform(int (*handler)(T *), T *context)
+{
+    return iothread_perform_base((int (*)(void *))handler, (void (*)(void *, int))0, static_cast<void *>(context));
+}
+
+template<typename T>
+int iothread_perform_on_main(int (*handler)(T *), T *context)
+{
+    return iothread_perform_on_main_base((int (*)(void *))handler, (void *)(context));
+}
+
+
+#endif