First pass at using Linkedom instead of microlink

[rknightuk]

Uses Linkedom and probe-image-size to get a similar set of same data without relying on a third party service.

Some quick tests show a big improvement in speed:

The 3 demo links:
microlink: 3.99 seconds
linkedom: 1.98 seconds

10 random links:
microlink: 20.36 seconds
linkedom: 5.80 seconds

Moving to this adds more chance of missing data, would be worth adding tests to cover each of the selectors.

Would also be worth investigating using the metascaper packages instead for getting the data.

Also includes the same changes that are in #3 (custom cache, updated readme)

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