Adds ThrowIfRector rule

[peterfox]

Changes

• Adds the new rule
• Adds tests for the rule
• Updates the Rule list

Why

I thought it would be a nice addition to be able to automatically convert simply if statements that are used to throw an exception.

Example code:

-if ($condition) {
-    throw new Exception();
-}
-if (!$condition) {
-    throw new Exception();
-}
+throw_if($condition, new Exception());
+throw_unless($condition, new Exception());