[ADD] librairy D3 v6

lib/d3-v6/LICENSE

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+Copyright 2010-2020 Mike Bostock
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+* Redistributions of source code must retain the above copyright notice, this
+  list of conditions and the following disclaimer.
+
+* Redistributions in binary form must reproduce the above copyright notice,
+  this list of conditions and the following disclaimer in the documentation
+  and/or other materials provided with the distribution.
+
+* Neither the name of the author nor the names of contributors may be used to
+  endorse or promote products derived from this software without specific prior
+  written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

lib/d3-v6/README.md

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+# D3: Data-Driven Documents
+
+<a href="https://d3js.org"><img src="https://d3js.org/logo.svg" align="left" hspace="10" vspace="6"></a>
+
+**D3** (or **D3.js**) is a JavaScript library for visualizing data using web standards. D3 helps you bring data to life using SVG, Canvas and HTML. D3 combines powerful visualization and interaction techniques with a data-driven approach to DOM manipulation, giving you the full capabilities of modern browsers and the freedom to design the right visual interface for your data.
+
+## Resources
+
+* [Introduction](https://observablehq.com/@d3/learn-d3)
+* [API Reference](https://github.com/d3/d3/blob/master/API.md)
+* [Releases](https://github.com/d3/d3/releases)
+* [Examples](https://observablehq.com/@d3/gallery)
+* [Wiki](https://github.com/d3/d3/wiki)
+
+## Installing
+
+If you use npm, `npm install d3`. Otherwise, download the [latest release](https://github.com/d3/d3/releases/latest). The released bundle supports anonymous AMD, CommonJS, and vanilla environments. You can load directly from [d3js.org](https://d3js.org), [CDNJS](https://cdnjs.com/libraries/d3), or [unpkg](https://unpkg.com/d3/). For example:
+
+```html
+<script src="https://d3js.org/d3.v6.js"></script>
+```
+
+For the minified version:
+
+```html
+<script src="https://d3js.org/d3.v6.min.js"></script>
+```
+
+You can also use the standalone D3 microlibraries. For example, [d3-selection](https://github.com/d3/d3-selection):
+
+```html
+<script src="https://d3js.org/d3-selection.v2.js"></script>
+```
+
+D3 is written using [ES2015 modules](http://www.2ality.com/2014/09/es6-modules-final.html). Create a [custom bundle using Rollup](https://bl.ocks.org/mbostock/bb09af4c39c79cffcde4), Webpack, or your preferred bundler. To import D3 into an ES2015 application, either import specific symbols from specific D3 modules:
+
+```js
+import {scaleLinear} from "d3-scale";
+```
+
+Or import everything into a namespace (here, `d3`):
+
+```js
+import * as d3 from "d3";
+```
+
+In Node:
+
+```js
+const d3 = require("d3");
+```
+
+You can also require individual modules and combine them into a `d3` object using [Object.assign](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign):
+
+```js
+const d3 = Object.assign({}, require("d3-format"), require("d3-geo"), require("d3-geo-projection"));
+```