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.

test/api/main.c

@@ -60,6 +60,6 @@ int main(int argc, const char* argv[])
   strcat(testPath, testName);
   strcat(testPath, ".wren");
 
-  runFile(bindForeign, testPath);
+  runFile(testPath, bindForeign);
   return 0;
 }