feat: make this plugin can run on non-maven project (wihtout pom.xml)

make this plugin goals can run on any project which has .editorconfig on project basedir

such as with -Deditorconfig.basedir
```
mvn org.ec4j.maven:editorconfig-maven-plugin:0.1.x:format -Deditorconfig.includes=**/*.xml -e -Deditorconfig.encoding=UTF-8 -Dproject.basedir=/any_dir_with_editorconfig
```
or

without editorconfig.basedir means on current dir
```
mvn org.ec4j.maven:editorconfig-maven-plugin:0.1.x:format -Deditorconfig.includes=**/*.xml -e -Deditorconfig.encoding=UTF-8
```
or

Author: qxo

editorconfig-maven-plugin/src/main/java/org/ec4j/maven/AbstractEditorConfigMojo.java

@@ -75,7 +75,7 @@ public abstract class AbstractEditorConfigMojo extends AbstractMojo {
      *
      * @since 0.0.1
      */
-    @Parameter(defaultValue = "${project.basedir}", required = true, readonly = true)
+    @Parameter(defaultValue = "${project.basedir}", required = false, readonly = true)
     private File basedir;
 
     /** The result of {@code basedir.toPath()} */
@@ -216,6 +216,9 @@ public void execute() throws MojoExecutionException, MojoFailureException {
         } else {
             this.charset = Charsets.forName(this.encoding);
         }
+        if (basedir == null) {
+            basedir = new File(".").getAbsoluteFile();
+        }
         this.basedirPath = basedir.toPath();
 
         LinterRegistry linterRegistry = buildLinterRegistry();

editorconfig-maven-plugin/src/main/java/org/ec4j/maven/EditorConfigCheckMojo.java

@@ -31,7 +31,7 @@
  * @since 0.0.1
  * @author <a href="https://github.com/ppalaga">Peter Palaga</a>
  */
-@Mojo(defaultPhase = LifecyclePhase.VERIFY, name = "check", threadSafe = true)
+@Mojo(requiresProject = false, defaultPhase = LifecyclePhase.VERIFY, name = "check", threadSafe = true)
 public class EditorConfigCheckMojo extends AbstractEditorConfigMojo {
 
     /**

editorconfig-maven-plugin/src/main/java/org/ec4j/maven/EditorConfigFormatMojo.java

@@ -29,7 +29,7 @@
  * @since 0.0.1
  * @author <a href="https://github.com/ppalaga">Peter Palaga</a>
  */
-@Mojo(defaultPhase = LifecyclePhase.NONE, name = "format", threadSafe = true)
+@Mojo(requiresProject = false, defaultPhase = LifecyclePhase.NONE, name = "format", threadSafe = true)
 public class EditorConfigFormatMojo extends AbstractEditorConfigMojo {
 
     /**