Switch license to MIT-0

[jwnimmer-tri]

Closes #240.

Relates to https://github.com/RobotLocomotion/drake/issues/1805 a bit.

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This change is 

[jwnimmer-tri]

Hello @yf225, @cjds, and @adeeb10abbas. Thank you for your past contributions to the drake-external-examples project (#106, #181, and #244)!

To make it easier for Drake's users to take advantage of these examples, I'd like to re-license this repository from the BSD-3-Clause license to the MIT-0 license. With the old license, users are required to preserve the examples' copyright notices in their own project, leading to a extra boilerplate and hassle. With the new license, users would not be required to copy over those comments when bootstrapping their build system.

As past contributors to this repository, I'm seeking your approval of this license change. Kindly please reply to this pull request, stating whether or not you approve of this change. Your approval would effectively re-license your contribution under the new terms.

[adeeb10abbas]

@jwnimmer-tri sounds good to me! Happy to help/contribute :)

[yf225]

Sounds good to me too, thanks!

[jwnimmer-tri]

I went back through the @cjds contribution and it was only https://github.com/RobotLocomotion/drake-external-examples/commit/95a34660d85c2a3c2788c4866da63badfb238eff.

I'll check whether or not any copyright there has bled into other files, and for now plan to switch everything except that contribution to MIT-0.

Update: Those two files were not copied anywhere else. So I'll just leave them alone for the moment. Once we age out Focal support, they will disappear.

[jwnimmer-tri]

Yay, and GitHub already noticed!

[cjds]

@sherm1 sorry for the late reply. Haven't been monitoring GitHub off late. Happy to contribute as well if applicable

[sherm1]

Thanks, Carl -- much appreciated. cc @jwnimmer-tri