Added php-cs-fixer configuration

this is by no means a complete code style guide, but it fixes a lot of common issues that show up, particularly in PRs.

.php_cs

@@ -0,0 +1,71 @@
+<?php
+
+$finder = PhpCsFixer\Finder::create()
+	->in(__DIR__ . '/src')
+	->in(__DIR__ . '/build')
+	->in(__DIR__ . '/tests')
+	->notPath('plugins/DevTools')
+	->notPath('preprocessor')
+	->notContains('#ifndef COMPILE') //preprocessor will break if these are changed
+	->notName('PocketMine.php');
+
+return PhpCsFixer\Config::create()
+	->setRiskyAllowed(true)
+	->setRules([
+		'align_multiline_comment' => [
+			'comment_type' => 'phpdocs_only'
+		],
+		'array_indentation' => true,
+		'array_syntax' => [
+			'syntax' => 'short'
+		],
+		'blank_line_after_namespace' => true,
+		'blank_line_after_opening_tag' => true,
+		'blank_line_before_statement' => [
+			'statements' => [
+				'declare'
+			]
+		],
+		'cast_spaces' => [
+			'space' => 'single'
+		],
+		'concat_space' => [
+			'spacing' => 'one'
+		],
+		'declare_strict_types' => true,
+		'elseif' => true,
+		'global_namespace_import' => [
+			'import_constants' => true,
+			'import_functions' => true,
+			'import_classes' => null,
+		],
+		'indentation_type' => true,
+		'native_function_invocation' => [
+		    'scope' => 'namespaced'
+		],
+		'no_closing_tag' => true,
+		'no_empty_phpdoc' => true,
+		'no_extra_blank_lines' => true,
+		'no_superfluous_phpdoc_tags' => [
+            'allow_mixed' => true,
+		],
+		'no_trailing_whitespace' => true,
+		'no_trailing_whitespace_in_comment' => true,
+		'no_whitespace_in_blank_line' => true,
+		'no_unused_imports' => true,
+		'ordered_imports' => [
+			'imports_order' => [
+				'class',
+				'function',
+				'const',
+			],
+			'sort_algorithm' => 'alpha'
+		],
+		'phpdoc_trim' => true,
+		'phpdoc_trim_consecutive_blank_line_separation' => true,
+		'single_import_per_statement' => true,
+		'strict_param' => true,
+	])
+	->setFinder($finder)
+	->setIndent("\t")
+	->setLineEnding("\n");