Feat invalidate transport

[nithril]

From https://github.com/nithril/smtp-connection-pool/pull/18 This PR adds the possibility to invalidate ClosableSmtpConnection instead of returning them in the pool.

My use case is:

• I do not want to testOnBorrow or testOnReturn since this impacts performance negatively
• If there is no exception when sending emails, return the connection to the pool, it appears to still be good
• If there is an exception, do not return the connection to the pool, it might be bad

[nithril]

@evigeant, could you please check if the commit https://github.com/nithril/smtp-connection-pool/commit/750d6b77c071ce828125ff9bb807ad3dbb0fbf7c is ok for you?

[evigeant]

Yes, it all makes sense, cleaned up the code nicely. I did not know, you could have this kind of code:

void test() throws SpecificException {
  try {
    // Code that throws SpecificException
  } catch(Exception e) {
    throw e;
  }
}

With older versions of the JDK, it would complain about the throws clause I believe, but I learned today that it works well... Thanks.

[nithril]

Released in 1.4.0