Clarify license of marching cubes implementation

[paulapatience]

I am going to port the C++ marching cubes implementation to another language and am seeking clarification with regards to its license. The repository's LICENSE.md consists of the MIT license, but the copyright notice of mc/MarchingCubes.h states the license as BSD-2, and that of mc/MarchingCubes.cpp has no accompanying license.

I assume that it is an oversight, as the license file was added after the marching cubes implementation, so presumably the intention is for the whole repository to be licensed under the MIT license, but it would be great if you could clarify that, possibly by removing the copyright notices of those files, or mentioning the MIT license therein.

If you wish to follow a standard convention, might I suggest something like the following:

// SPDX-FileCopyrightText: Copyright (c) 2016 Roberto Grosso
// SPDX-License-Identifier: MIT