Hyperlink support for cells

[speedytwenty]

This PR adds support for hyperlinks using a very simple interface. This feature was requested in #73

table.push([
  // Specify the URL as the display text
  { href: 'http://example.com' }, 
  // Specify display text
  { href: 'http://example.com', content: 'Example text' },
]);

Link text is wrapped, truncated, etc. as usual but when the text of a cell spans multiple lines, each line is wrapped with the link.

PR includes:

• Added utils.hyplerink() with unit tests (with credits to @matheussampaio)
• Added hyperlink support to Cell with functional tests that generate documentation
• Updated documentation basic-usage.md

The difference in functionality is not meaningfully demonstrable in markdown. Examine the (failing/passing) tests in Checks to inspect the differences.