Added read, list, search methods for numbers API

[ghost]

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[epels]

Hey Fredy, thanks for the PR! I have left some comments

[epels]

Thanks, looks good in general! Left a few comments.

Some more general remarks:

• godoc comments are typically full sentences ending in a period.
• It appears not all code has been run through gofmt, and most files have no trailing new line at EOF. It's probably worthwhile setting up your editors to enforce these.
• Looks like you default to Fatalf in all tests, but in many cases test output can be more useful when used with Errorf. Personally, I only use Fatalf when it makes no sense to continue the rest of the test. E.g. here, it is still useful to assert the query string - even if the response object's country code doesn't match.