Support labelled links format for SQLite/Datasette

[anjackson]

Support labels for the links field in datasette-lite via plugins.

The current list of links is a simple key-value pair. It could be formatted as a label and a href, as per https://datasette.io/plugins/datasette-json-html and then a link like

https://lite.datasette.io/?install=datasette-json-html#/fixtures?sql=select+%27%5B%0A++++%7B%0A++++++++%22href%22%3A+%22https%3A%2F%2Fsimonwillison.net%2F%22%2C%0A++++++++%22label%22%3A+%22Simon+Willison%22%0A++++%7D%2C%0A++++%7B%0A++++++++%22href%22%3A+%22https%3A%2F%2Fgithub.com%2Fsimonw%2Fdatasette%22%2C%0A++++++++%22label%22%3A+%22Datasette%22%0A++++%7D%0A%5D%27+as+output

Can be used to install the module in Datasette Lite and make use of it to 'pretty print' the links field.