Reorganize documentation & update Readme

docs/Base-test-case.md

@@ -0,0 +1,50 @@
+# Meritoo Common Library
+Common and useful classes, methods, exceptions etc.
+
+# Base test case (with common methods and data providers)
+
+Located here: `Meritoo\Common\Test\Base\BaseTestCase`. Just extend the `BaseTestCase` class and use it like in `Meritoo\Common\Test\Utilities\DateTest` class:
+
+```php
+class DateTest extends BaseTestCase
+{
+    /**
+     * @param mixed $value Empty value, e.g. ""
+     * @dataProvider provideEmptyValue
+     */
+    public function testGetDateTimeEmptyValue($value)
+    {
+        self::assertFalse(Date::getDateTime($value));
+    }
+
+	(...)
+}
+```
+
+or in `Meritoo\Common\Test\Utilities\MimeTypesTest` class:
+
+```php
+class MimeTypesTest extends BaseTestCase
+{
+	(...)
+
+    /**
+     * @param bool $mimeType The mime type, e.g. "video/mpeg"
+     * @dataProvider provideBooleanValue
+     */
+    public function testGetExtensionBooleanMimeType($mimeType)
+    {
+        self::assertEquals('', MimeTypes::getExtension($mimeType));
+    }
+
+	(...)
+}
+```
+
+# More
+
+1. [**Base test case (with common methods and data providers)**](Base-test-case.md)
+2. [Collection of elements](Collection-of-elements.md)
+3. [Static methods](Static-methods.md)
+
+[‹ Back to `Readme`](../README.md)