As requested by the reviewer PR updated in order to fix API duplication and missing https for hubblesite.

Add NBP (National Bank of Poland) currency exchange rates API

Changed waifu.pics url

changed to to api docs in stead of main page

Added Visual Crossing Weather API

Indeed has discontinued their API. See https://stackoverflow.com/a/66036140/13752077

The PR #1610 added an duplicate link to the government section

The PR #1610 added an extra blank line

This isn't an API but rather the site where they are collated by the UK
government.

I've added the data.gov.uk site as a separate entry for clarity (because
of the number of similar sites from other countries). This site is also
linked to from the API catalogue site.

Removed .com from wecantrack.com

Fixes the issue #1307

The links https://plino.herokuapp.com and https://sentim-api.herokuapp.com were broken

Mozilla Observatory ordered alphabetically

This description broken tests:

- description should not end with .
- description should not exceed 100 characters (currently 131)

Close #1095

Close #999

Closes #1597