feat: include all endpoints

* Reworked interfacing to drop the versioning in the class name.
* Refactored / cleaned up existing code.
* Stuck with support for PHP 5.3+ since PHP 5.x still seems to hold majority.
* Abstracted request logic to another class for mocking.
* Added test suite and hit full code coverage.
* Updated readme, included migration guide and the full gamut of examples.
* Wired up travis-ci and coveralls for testing and coverage.

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="Holiday API">
+      <directory>tests</directory>
+    </testsuite>
+  </testsuites>
+  <filter>
+    <whitelist addUncoveredFilesFromWhitelist="true">
+      <directory>./src</directory>
+    </whitelist>
+  </filter>
+</phpunit>