use PSR-2 coding standard (for now) #4

* require squizlabs/php_codesniffer
* add .phpcs.xml
* update README.md
* add composer scripts for validations
* ignore .phpcs.xml on git export

Author: gregor-j

.gitattributes

@@ -2,5 +2,6 @@
 .gitattributes  export-ignore
 .github			export-ignore
 .gitignore      export-ignore
+.phpcs.xml		export-ignore
 composer.*      export-ignore
 README.md       export-ignore

.phpcs.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0"?>
+<ruleset name="PSR2" namespace="PHP-SAP\Standards">
+    <description>PHP/SAP PSR2 programming standard</description>
+    <!-- display progress -->
+    <arg value="p"/>
+    <arg value="n"/>
+    <!-- directories and files to check -->
+    <file>./src</file>
+    <!-- Use PSR2 as a standard -->
+    <rule ref="PSR2">
+    </rule>
+</ruleset>

README.md

@@ -4,5 +4,12 @@
 
 This repository defines interfaces for implementing the [PHP/SAP][phpsap] API.
 
+## Coding standards
+
+This project uses [PSR-2] coding standard and [PHP_CodeSniffer] for validations.
+In order to validate before a commit, call `vendor/bin/phpcs`.
+
 [phpsap]: https://php-sap.github.io
 [license-mit]: https://img.shields.io/badge/license-MIT-blue.svg
+[PSR-2]: https://www.php-fig.org/psr/psr-2/
+[PHP_CodeSniffer]: https://github.com/squizlabs/PHP_CodeSniffer

composer.json

@@ -28,5 +28,16 @@
     "psr-4": {
       "phpsap\\interfaces\\": "src/"
     }
+  },
+  "require-dev": {
+    "squizlabs/php_codesniffer": "^3.7"
+  },
+  "scripts": {
+    "phpcs": "vendor/bin/phpcs",
+    "phpcbf": "vendor/bin/phpcbf"
+  },
+  "scripts-descriptions": {
+    "phpcs": "Run PHP CodeSniffer validations.",
+    "phpcbf": "Fix errors found by PHP CodeSniffer."
   }
 }