#1497 Show specific message for invalid YAML files (#1506)

* #1497 Throw dedicated exception for invalid YAML files and handle it on startup
- Wrap SnakeYAML exceptions when loading config.yml and commands.yml on startup into own exception type
- Handle exception type on startup with specific error message

* #1497 Fix inaccurate JavaDoc comment

src/main/java/fr/xephi/authme/service/yaml/YamlFileResourceProvider.java

@@ -0,0 +1,30 @@
+package fr.xephi.authme.service.yaml;
+
+import ch.jalu.configme.resource.YamlFileResource;
+import org.yaml.snakeyaml.parser.ParserException;
+
+import java.io.File;
+
+/**
+ * Creates {@link YamlFileResource} objects.
+ */
+public final class YamlFileResourceProvider {
+
+    private YamlFileResourceProvider() {
+    }
+
+    /**
+     * Creates a {@link YamlFileResource} instance for the given file. Wraps SnakeYAML's parse exception
+     * into an AuthMe exception.
+     *
+     * @param file the file to load
+     * @return the generated resource
+     */
+    public static YamlFileResource loadFromFile(File file) {
+        try {
+            return new YamlFileResource(file);
+        } catch (ParserException e) {
+            throw new YamlParseException(file.getPath(), e);
+        }
+    }
+}

src/main/java/fr/xephi/authme/service/yaml/YamlParseException.java

@@ -0,0 +1,26 @@
+package fr.xephi.authme.service.yaml;
+
+import org.yaml.snakeyaml.parser.ParserException;
+
+/**
+ * Exception when a YAML file could not be parsed.
+ */
+public class YamlParseException extends RuntimeException {
+
+    private final String file;
+
+    /**
+     * Constructor.
+     *
+     * @param file the file a parsing exception occurred with
+     * @param snakeYamlException the caught exception from SnakeYAML
+     */
+    public YamlParseException(String file, ParserException snakeYamlException) {
+        super(snakeYamlException);
+        this.file = file;
+    }
+
+    public String getFile() {
+        return file;
+    }
+}