Add pear modules, mail and net_smtp via composer (#93)

Add pear modules, mail and net_smtp via composer, remove php 5.6 build due to phpunit 6

lib/composer/vendor/pear/mail/tests/bug17178.phpt

@@ -0,0 +1,11 @@
+--TEST--
+Mail_RFC822::parseAddressList does not accept RFC-valid group syntax
+--FILE--
+<?php
+require "Mail/RFC822.php";
+
+var_dump(Mail_RFC822::parseAddressList("empty-group:;","invalid",false,false)); 
+
+--EXPECT--
+array(0) {
+}