Added last weight measures (#37)

* Added last weight measures

* Fixed stone units

src/UnitConverter/Unit/Mass/Stone.php

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+<?php
+
+/**
+ * This file is part of the jordanbrauer/unit-converter PHP package.
+ *
+ * @copyright 2017 Jordan Brauer <[email protected]>
+ * @license MIT
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types = 1);
+
+namespace UnitConverter\Unit\Mass;
+
+/**
+ * Stone data class.
+ *
+ * @version 1.0.0
+ * @since 1.0.0
+ * @author Jordan Brauer <[email protected]>
+ */
+class Stone extends MassUnit
+{
+    protected function configure () : void
+    {
+        $this
+            ->setName("stone")
+
+            ->setSymbol("st")
+
+            ->setUnits(6.35029)
+        ;
+    }
+}

src/UnitConverter/Unit/Mass/UKLongTon.php

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+<?php
+
+/**
+ * This file is part of the jordanbrauer/unit-converter PHP package.
+ *
+ * @copyright 2017 Jordan Brauer <[email protected]>
+ * @license MIT
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types = 1);
+
+namespace UnitConverter\Unit\Mass;
+
+/**
+ * UKLongTon data class.
+ *
+ * @version 1.0.0
+ * @since 1.0.0
+ * @author Jordan Brauer <[email protected]>
+ */
+class UKLongTon extends MassUnit
+{
+    protected function configure () : void
+    {
+        $this
+            ->setName("UK Long Ton")
+
+            ->setSymbol("ukt")
+
+            ->setUnits(2.204623)
+        ;
+    }
+}

src/UnitConverter/Unit/Mass/USShortTon.php

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+<?php
+
+/**
+ * This file is part of the jordanbrauer/unit-converter PHP package.
+ *
+ * @copyright 2017 Jordan Brauer <[email protected]>
+ * @license MIT
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+declare(strict_types = 1);
+
+namespace UnitConverter\Unit\Mass;
+
+/**
+ * USShortTon data class.
+ *
+ * @version 1.0.0
+ * @since 1.0.0
+ * @author Jordan Brauer <[email protected]>
+ */
+class USShortTon extends MassUnit
+{
+    protected function configure () : void
+    {
+        $this
+            ->setName("US Short Ton")
+
+            ->setSymbol("ust")
+
+            ->setUnits(2.204623)
+        ;
+    }
+}