d3.js, Force Layout primer

For study purposes only

• Cleaned up an example from : https://bl.ocks.org/mbostock/1095795/8f34afdd6d321b71ca6b3a5904e486f3173f1111
• Cleaned up example uses d3 version 5.
• Original example license : https://opensource.org/licenses/GPL-3.0
• Original example uses d3 version 4.

fork and updated from from https://bl.ocks.org/jerng/b47cf70fc0fd20ccf56cdb42e172e877