A vertical slice of real libuv integration.

This adds a "timer" module to the CLI that provides a Timer class with
a static sleep() method. Not the most exciting functionality in the
world, but it requires the full hunk of libuv integration:

- The CLI sets up libuv and runs the event loop.
- Added a new directory src/module for CLI modules.
- Updated all the make scripts to handle it.
- Reorganized some other CLI code.

src/module/timer.c

@@ -0,0 +1,81 @@
+#include <stdlib.h>
+#include <string.h>
+
+#include "uv.h"
+
+#include "timer.h"
+#include "wren.h"
+#include "vm.h"
+
+// This is generated from builtin/module/timer.wren. Do not edit here.
+static const char* timerLibSource =
+"class Timer {\n"
+"  static sleep(milliseconds) {\n"
+"    startTimer_(milliseconds, Fiber.current)\n"
+"    Fiber.yield()\n"
+"  }\n"
+"\n"
+"  foreign static startTimer_(milliseconds, fiber)\n"
+"\n"
+"  // Called by native code.\n"
+"  static resumeTimer_(fiber) {\n"
+"    fiber.run()\n"
+"  }\n"
+"}\n";
+
+// The Wren method to call when a timer has completed.
+static WrenMethod* resumeTimer;
+
+// Called by libuv when the timer has completed.
+static void timerCallback(uv_timer_t* handle)
+{
+  WrenValue* fiber = (WrenValue*)handle->data;
+  free(handle);
+
+  // Run the fiber that was sleeping.
+  wrenCall(getVM(), resumeTimer, "v", fiber);
+  wrenReleaseValue(getVM(), fiber);
+}
+
+static void startTimer(WrenVM* vm)
+{
+  // If we haven't looked up the resume method yet, grab it now.
+  if (resumeTimer == NULL)
+  {
+    resumeTimer = wrenGetMethod(vm, "timer", "Timer", "resumeTimer_(_)");
+  }
+  
+  int milliseconds = (int)wrenGetArgumentDouble(vm, 1);
+  WrenValue* fiber = wrenGetArgumentValue(vm, 2);
+  
+  // Store the fiber to resume when the timer completes.
+  uv_timer_t* handle = (uv_timer_t*)malloc(sizeof(uv_timer_t));
+  handle->data = fiber;
+  
+  uv_timer_init(getLoop(), handle);
+  uv_timer_start(handle, timerCallback, milliseconds, 0);
+}
+
+char* timerGetSource()
+{
+  size_t length = strlen(timerLibSource);
+  char* copy = malloc(length + 1);
+  strncpy(copy, timerLibSource, length);
+  
+  return copy;
+}
+
+WrenForeignMethodFn timerBindForeign(
+    WrenVM* vm, const char* className, bool isStatic, const char* signature)
+{
+  if (strcmp(className, "Timer") != 0) return NULL;
+
+  if (isStatic && strcmp(signature, "startTimer_(_,_)") == 0) return startTimer;
+  
+  return NULL;
+}
+
+void timerReleaseMethods()
+{
+  if (resumeTimer != NULL) wrenReleaseMethod(getVM(), resumeTimer);
+}

src/module/timer.h

@@ -0,0 +1,14 @@
+#ifndef timer_h
+#define timer_h
+
+#include "wren.h"
+
+// TODO: Coherent naming scheme.
+char* timerGetSource();
+
+WrenForeignMethodFn timerBindForeign(
+    WrenVM* vm, const char* className, bool isStatic, const char* signature);
+
+void timerReleaseMethods();
+
+#endif

src/module/timer.wren

@@ -0,0 +1,13 @@
+class Timer {
+  static sleep(milliseconds) {
+    startTimer_(milliseconds, Fiber.current)
+    Fiber.yield()
+  }
+
+  foreign static startTimer_(milliseconds, fiber)
+
+  // Called by native code.
+  static resumeTimer_(fiber) {
+    fiber.run()
+  }
+}