ci: add newer PHP versions

Seems I had started this a while back and never actually finished.
Bumped the copyright years and added a funding and git ignore file.
Redid the Travis configuration based on my more recent experiences with
testing multiple PHP versions. Updated the development dependencies and
added a configuration file for PHPUnit.

phpunit.xml

@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit
+  colors="true"
+  convertErrorsToExceptions="true"
+  convertNoticesToExceptions="true"
+  convertWarningsToExceptions="true"
+  failOnRisky="true"
+  stopOnError="true"
+  stopOnFailure="true"
+  stopOnIncomplete="true"
+  verbose="true"
+>
+  <testsuites>
+    <testsuite name="Project Honey Pot">
+      <directory>tests</directory>
+    </testsuite>
+  </testsuites>
+  <filter>
+    <whitelist addUncoveredFilesFromWhitelist="true">
+      <directory>./src</directory>
+    </whitelist>
+  </filter>
+</phpunit>