Building igl statically and moving to the dep scripts

Fixing dep build script on Windows and removing some warnings.

Use bundled igl by default.

Not building with the dependency scripts if not explicitly stated. This way, it will stay in
Fix the libigl patch to include C source files in header only mode.

src/libigl/igl/png/render_to_png_async.cpp

@@ -0,0 +1,54 @@
+// This file is part of libigl, a simple c++ geometry processing library.
+//
+// Copyright (C) 2013 Alec Jacobson <alecjacobson@gmail.com>
+//
+// This Source Code Form is subject to the terms of the Mozilla Public License
+// v. 2.0. If a copy of the MPL was not distributed with this file, You can
+// obtain one at http://mozilla.org/MPL/2.0/.
+#include "render_to_png_async.h"
+#include "../opengl/gl.h"
+#include <igl_stb_image.h>
+
+static IGL_INLINE bool render_to_png_async_helper(
+  unsigned char * img, int width, int height,
+  const std::string png_file,
+  const bool alpha,
+  const bool fast)
+{
+  //img->flip();
+  if(!alpha)
+  {
+    for(int i = 0;i<width;i++)
+    for(int j = 0;j<height;j++)
+    {
+      img[4*(i+j*width)+3] = 255;
+    }
+  }
+
+  bool ret = igl::stbi_write_png(png_file.c_str(), width, height, 4, img, width*sizeof(unsigned char));
+  delete [] img;
+  return ret;
+}
+
+IGL_INLINE std::thread igl::png::render_to_png_async(
+  const std::string png_file,
+  const int width,
+  const int height,
+  const bool alpha,
+  const bool fast)
+{
+  // Part that should serial
+  unsigned char * data = new unsigned char[width*height];
+  glReadPixels(
+    0,
+    0,
+    width,
+    height,
+    GL_RGBA,
+    GL_UNSIGNED_BYTE,
+    data);
+  // Part that should be asynchronous
+  std::thread t(render_to_png_async_helper,data,width,height,png_file,alpha,fast);
+  t.detach();
+  return t;
+}