Fix email nested in link text, add some basic tests

[teppokoivula]

@Roope, sorry! I didn't test previous PR well enough. Found an issue with nested emails.

Things looked fine at first glance, but actually...

<a href="https://example.com/example@example.com">https://example.com/example@example.com</a>

... resulted in something like this:

<a href="https://example.com/example@example.com">https://example.com/<noscript data-emo=\"PGEgaHJlZj0ibWFpbHRvOnVzZXJAZG9tYWluLmNvbSI_dXNlckBkb21haW4uY29tPC9hPgAA\">Enable JavaScript to view protected
  content.</noscript></a>

This should now be fixed in this PR.

Also, since this is actually a tiny bit complicated, I thought it might make sense to bundle in some basic tests. testObfuscation($html) can be used for one-off tests, and testObfuscationWithCases() runs some predefined test cases. Feel free to discard this part if you don't like the idea, but it helped me a lot while testing different situations :)

Test results are an array like this:

  {
      "plain email": {
          "pass": true,
          "input": "Contact us at test@example.com for help.",
          "output": "Contact us at <noscript data-emo=\"PGEgaHJlZj0ibWFpbHRvOnRlc3RAZXhhbXBsZS5jb20iPnRlc3RAZXhhbXBsZS5jb208L2E_\">Enable JavaScript to view protected content.</noscript> for help.",
          "expected": "Contact us at <noscript data-emo=\"PGEgaHJlZj0ibWFpbHRvOnRlc3RAZXhhbXBsZS5jb20iPnRlc3RAZXhhbXBsZS5jb208L2E_\">Enable JavaScript to view protected content.</noscript> for help."
      },
      "mailto link": {
          "pass": true,
          "input": "<a href=\"mailto:test@example.com\">test@example.com</a>",
          "output": "<noscript data-emo=\"PGEgaHJlZj0ibWFpbHRvOnRlc3RAZXhhbXBsZS5jb20iPnRlc3RAZXhhbXBsZS5jb208L2E_\">Enable JavaScript to view protected content.</noscript>",
          "expected": "<noscript data-emo=\"PGEgaHJlZj0ibWFpbHRvOnRlc3RAZXhhbXBsZS5jb20iPnRlc3RAZXhhbXBsZS5jb208L2E_\">Enable JavaScript to view protected content.</noscript>"
      },
      "url with email-like path": {
          "pass": true,
          "input": "<a href=\"https://example.com/user@domain.com\">https://example.com/user@domain.com</a>",
          "output": "<a href=\"https://example.com/user@domain.com\">https://example.com/user@domain.com</a>",
          "expected": "<a href=\"https://example.com/user@domain.com\">https://example.com/user@domain.com</a>"
      },
      "email query parameter": {
          "pass": true,
          "input": "<a href=\"https://example.com/?email=user@example.com\">https://example.com/?email=user@example.com</a>",
          "output": "<a href=\"https://example.com/?email=user@example.com\">https://example.com/?email=user@example.com</a>",
          "expected": "<a href=\"https://example.com/?email=user@example.com\">https://example.com/?email=user@example.com</a>"
      },
      "multiple emails": {
          "pass": true,
          "input": "Contact alice@example.com or bob@example.com for help.",
          "output": "Contact <noscript data-emo=\"PGEgaHJlZj0ibWFpbHRvOmFsaWNlQGV4YW1wbGUuY29tIj5hbGljZUBleGFtcGxlLmNvbTwvYT4A\">Enable JavaScript to view protected content.</noscript> or <noscript
  data-emo=\"PGEgaHJlZj0ibWFpbHRvOmJvYkBleGFtcGxlLmNvbSI_Ym9iQGV4YW1wbGUuY29tPC9hPgAA\">Enable JavaScript to view protected content.</noscript> for help.",
          "expected": "Contact <noscript data-emo=\"PGEgaHJlZj0ibWFpbHRvOmFsaWNlQGV4YW1wbGUuY29tIj5hbGljZUBleGFtcGxlLmNvbTwvYT4A\">Enable JavaScript to view protected content.</noscript> or <noscript
  data-emo=\"PGEgaHJlZj0ibWFpbHRvOmJvYkBleGFtcGxlLmNvbSI_Ym9iQGV4YW1wbGUuY29tPC9hPgAA\">Enable JavaScript to view protected content.</noscript> for help."
      }
  }

And without this fix, two of the tests would fail:

      "url with email-like path": {
          "pass": false,
          "input": "<a href=\"https://example.com/user@domain.com\">https://example.com/user@domain.com</a>",
          "output": "<a href=\"https://example.com/user@domain.com\">https://example.com/<noscript data-emo=\"PGEgaHJlZj0ibWFpbHRvOnVzZXJAZG9tYWluLmNvbSI_dXNlckBkb21haW4uY29tPC9hPgAA\">Enable JavaScript to view protected
  content.</noscript></a>",
          "expected": "<a href=\"https://example.com/user@domain.com\">https://example.com/user@domain.com</a>"
      },
      "email query parameter": {
          "pass": false,
          "input": "<a href=\"https://example.com/?email=user@example.com\">https://example.com/?email=user@example.com</a>",
          "output": "<a href=\"https://example.com/?email=user@example.com\">https://example.com/<noscript data-emo=\"PGEgaHJlZj0ibWFpbHRvOj9lbWFpbD11c2VyQGV4YW1wbGUuY29tIj4.ZW1haWw9dXNlckBleGFtcGxlLmNvbTwvYT4A\">Enable JavaScript to view
   protected content.</noscript></a>",
          "expected": "<a href=\"https://example.com/?email=user@example.com\">https://example.com/?email=user@example.com</a>"
      },