This relicenses Bevy under the dual MIT or Apache-2.0 license. For rationale, see #2373.
* Changes the LICENSE file to describe the dual license. Moved the MIT license to docs/LICENSE-MIT. Added the Apache-2.0 license to docs/LICENSE-APACHE. I opted for this approach over dumping both license files at the root (the more common approach) for a number of reasons:
* Github links to the "first" license file (LICENSE-APACHE) in its license links (you can see this in the wgpu and rust-analyzer repos). People clicking these links might erroneously think that the apache license is the only option. Rust and Amethyst both use COPYRIGHT or COPYING files to solve this problem, but this creates more file noise (if you do everything at the root) and the naming feels way less intuitive.
* People have a reflex to look for a LICENSE file. By providing a single license file at the root, we make it easy for them to understand our licensing approach.
* I like keeping the root clean and noise free
* There is precedent for putting the apache and mit license text in sub folders (amethyst)
* Removed the `Copyright (c) 2020 Carter Anderson` copyright notice from the MIT license. I don't care about this attribution, it might make license compliance more difficult in some cases, and it didn't properly attribute other contributors. We shoudn't replace it with something like "Copyright (c) 2021 Bevy Contributors" because "Bevy Contributors" is not a legal entity. Instead, we just won't include the copyright line (which has precedent ... Rust also uses this approach).
* Updates crates to use the new "MIT OR Apache-2.0" license value
* Removes the old legion-transform license file from bevy_transform. bevy_transform has been its own, fully custom implementation for a long time and that license no longer applies.
* Added a License section to the main readme
* Updated our Bevy Plugin licensing guidelines.
As a follow-up we should update the website to properly describe the new license.
Closes#2373
Updates the requirements on [wgpu](https://github.com/gfx-rs/wgpu) to permit the latest version.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/gfx-rs/wgpu/blob/master/CHANGELOG.md">wgpu's changelog</a>.</em></p>
<blockquote>
<h1>Change Log</h1>
<h2>v0.9 (2021-06-18)</h2>
<ul>
<li>Updated:
<ul>
<li>naga to <code>v0.5</code>.</li>
</ul>
</li>
<li>Added:
<ul>
<li><code>Features::VERTEX_WRITABLE_STORAGE</code>.</li>
<li><code>Features::CLEAR_COMMANDS</code> which allows you to use <code>cmd_buf.clear_texture</code> and <code>cmd_buf.clear_buffer</code>.</li>
</ul>
</li>
<li>Changed:
<ul>
<li>Updated default storage buffer/image limit to <code>8</code> from <code>4</code>.</li>
</ul>
</li>
<li>Fixed:
<ul>
<li><code>Buffer::get_mapped_range</code> can now have a range of zero.</li>
<li>Fixed output spirv requiring the "kernal" capability.</li>
<li>Fixed segfault due to improper drop order.</li>
<li>Fixed incorrect dynamic stencil reference for Replace ops.</li>
<li>Fixed tracking of temporary resources.</li>
<li>Stopped unconditionally adding cubemap flags when the backend doesn't support cubemaps.</li>
</ul>
</li>
<li>Validation:
<ul>
<li>Ensure that if resources are viewed from the vertex stage, they are read only unless <code>Features::VERTEX_WRITABLE_STORAGE</code> is true.</li>
<li>Ensure storage class (i.e. storage vs uniform) is consistent between the shader and the pipeline layout.</li>
<li>Error when a color texture is used as a depth/stencil texture.</li>
<li>Check that pipeline output formats are logical</li>
<li>Added shader label to log messages if validation fails.</li>
</ul>
</li>
<li>Tracing:
<ul>
<li>Make renderpasses show up in the trace before they are run.</li>
</ul>
</li>
<li>Docs:
<ul>
<li>Fix typo in <code>PowerPreference::LowPower</code> description.</li>
</ul>
</li>
<li>Player:
<ul>
<li>Automatically start and stop RenderDoc captures.</li>
</ul>
</li>
<li>Examples:
<ul>
<li>Handle winit's unconditional exception.</li>
</ul>
</li>
<li>Internal:
<ul>
<li>Merged wgpu-rs and wgpu back into a single repository.</li>
<li>The tracker was split into two different stateful/stateless trackers to reduce overhead.</li>
<li>Added code coverage testing</li>
<li>CI can now test on lavapipe</li>
<li>Add missing extern "C" in wgpu-core on <code>wgpu_render_pass_execute_bundles</code></li>
<li>Fix incorrect function name <code>wgpu_render_pass_bundle_indexed_indirect</code> to <code>wgpu_render_bundle_draw_indexed_indirect</code>.</li>
</ul>
</li>
</ul>
<h2>wgpu-types-0.8.1 (2021-06-08)</h2>
<ul>
<li>fix dynamic stencil reference for Replace ops</li>
</ul>
<h2>v0.8.1 (2021-05-06)</h2>
<ul>
<li>fix SPIR-V generation from WGSL, which was broken due to "Kernel" capability</li>
<li>validate buffer storage classes</li>
</ul>
<h2>Unreleased</h2>
<ul>
<li>Added support for storage texture arrays for Vulkan and Metal.</li>
</ul>
<h2>v0.8 (2021-04-29)</h2>
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</blockquote>
<p>... (truncated)</p>
</details>
<details>
<summary>Commits</summary>
<ul>
<li>See full diff in <a href="https://github.com/gfx-rs/wgpu/commits">compare view</a></li>
</ul>
</details>
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</details>
Changes to get Bevy to compile with wgpu master.
With this, on a Mac:
* 2d examples look fine
* ~~3d examples crash with an error specific to metal about a compilation error~~
* 3d examples work fine after enabling feature `wgpu/cross`
Feature `wgpu/cross` seems to be needed only on some platforms, not sure how to know which. It was introduced in https://github.com/gfx-rs/wgpu-rs/pull/826
