Drop the internal intdiv polyfill

The library doesn't actually use the method that requires the
`intdiv()` function so it can be an optional dependency for users.

composer.json

@@ -21,8 +21,13 @@
     },
     "require-dev": {
         "cs278/coding-standard": "^1",
+        "michaelc/intdiv-compat": "^1.0.1",
         "phpunit/phpunit": "^4.8.21"
     },
+    "suggest": {
+        "michaelc/intdiv-compat": "Provides intdiv() which is needed if you use the modulus algorithms yourself.",
+        "symfony/polyfill-php70": "Provides intdiv() which is needed if you use the modulus algorithms yourself."
+    },
     "autoload": {
         "psr-4": {
             "Cs278\\BankModulus\\": "src/"

src/ModulusAlgorithm/BaseAlgorithm.php

@@ -21,19 +21,21 @@ public function __construct($result, $divisor)
     /** @return int */
     final public function quotient()
     {
-        if (null === self::$ourIntdiv) {
-            self::$ourIntdiv = !function_exists('intdiv');
-
-            if (self::$ourIntdiv && !function_exists('Cs278\BankModulus\intdiv')) {
-                require __DIR__.'/../intdiv.php';
-            }
+        if (!function_exists('intdiv')) {
+            // This method isn't actually used internally by the library
+            // currently so no hard dependency on these polyfills.
+
+            // @codeCoverageIgnoreStart
+            throw new \LogicException(sprintf(
+                '%s() requires the intdiv() function which was added in PHP 7'
+                .' you could use a polyfill such as michaelc/intdiv-compat or'
+                .' symfony/polyfill-php70 to provide this function',
+                __METHOD__
+            ));
+            // @codeCoverageIgnoreEnd
         }
 
-        if (self::$ourIntdiv) {
-            return \Cs278\BankModulus\intdiv($this->result, $this->divisor);
-        } else {
-            return intdiv($this->result, $this->divisor);
-        }
+        return intdiv($this->result, $this->divisor);
     }
 
     /** @return int */