Refactor folder (#10475)

Move many third-party components' source codes from the src folder to a new folder called deps_src. The goal is to make the code structure clearer and easier to navigate.

deps_src/libigl/igl/matlab/requires_arg.cpp

@@ -0,0 +1,16 @@
+// This file is part of libigl, a simple c++ geometry processing library.
+// 
+// Copyright (C) 2015 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 "requires_arg.h"
+#include "mexErrMsgTxt.h"
+#include "../C_STR.h"
+
+IGL_INLINE void igl::matlab::requires_arg(const int i, const int nrhs, const char *name)
+{
+  mexErrMsgTxt((i+1)<nrhs,
+      C_STR("Parameter '"<<name<<"' requires argument"));
+}