Coding style: switch PHPCS to PSR12

Also temporarily ignore test code (one step at a time).

Reference: https://www.php-fig.org/psr/psr-12/

Related to #95

Makefile

@@ -27,10 +27,6 @@ PHPCS := $(BIN)/phpcs
 code_sniffer:
 	@$(PHPCS)
 
-### - errors filtered by coding standard: PEAR, PSR1, PSR2, Zend...
-PHPCS_%:
-	@$(PHPCS) --report-full --report-width=200 --standard=$*
-
 ### - errors by Git author
 code_sniffer_blame:
 	@$(PHPCS) --report-gitblame

phpcs.xml

@@ -5,13 +5,13 @@
   <file>index.php</file>
   <file>application</file>
   <file>plugins</file>
-  <file>tests</file>
+<!--  <file>tests</file>-->
 
   <exclude-pattern>*/*.css</exclude-pattern>
   <exclude-pattern>*/*.js</exclude-pattern>
 
   <arg name="colors"/>
 
-  <rule ref="PSR1"/>
-  <rule ref="PSR2"/>
+  <rule ref="PSR12"/>
+  <rule ref="Generic.Arrays.DisallowLongArraySyntax"/>
 </ruleset>