Update W3C links
Revert 6e983607ae9942b76e67154088694940c32d57fe ... 1f100ca3b7777101dff9d66b5cf6016ef72b5a3e on Selections
Change W3C link
Updated Selections (markdown)
Revert 16f526b14def27329997c7fade5cb98b98539c40^ ... 16f526b14def27329997c7fade5cb98b98539c40
Destroyed Selections (markdown)
a note about using insert to prepend (practical example)
square brackets messed up section on selection.transition.
Revert b51b85c7344349b0ab5898f3cd65eeb6263a942a ... 877f86e6c1dc4a2ef2ffdc698dd620c0f52ea2b9
fix link to `datum` instead of `map`
Selectors should have double quotes, not code escapes.