Improve some javadocs (#683)

* Document more PebbleEngine.Builder() defaults

* Improve Loader javadoc

* Document AttributeResolver

pebble/src/main/java/io/pebbletemplates/pebble/PebbleEngine.java

@@ -442,9 +442,10 @@ public Builder tagCache(PebbleCache<CacheKey, Object> tagCache) {
     }
 
     /**
-     * Sets whether or not escaping should be performed automatically.
+     * Sets whether or not escaping should be performed automatically. The default value of this
+     * setting is "true".
      *
-     * @param autoEscaping The auto escaping setting
+     * @param autoEscaping The auto escaping setting.
      * @return This builder object
      */
     public Builder autoEscaping(boolean autoEscaping) {
@@ -453,7 +454,8 @@ public Builder autoEscaping(boolean autoEscaping) {
     }
 
     /**
-     * Sets whether or not core operators overrides should be allowed.
+     * Sets whether or not core operators overrides should be allowed. The default value of this
+     * setting is "false".
      *
      * @param allowOverrideCoreOperators Whether or not core operators overrides should be allowed.
      * @return This builder object
@@ -488,7 +490,7 @@ public Builder addEscapingStrategy(String name, EscapingStrategy strategy) {
 
     /**
      * Enable/disable all caches, i.e. cache used by the engine to store compiled PebbleTemplate
-     * instances and tags cache
+     * instances and tags cache. The default value of this setting is "true".
      *
      * @param cacheActive toggle to enable/disable all caches
      * @return This builder object

pebble/src/main/java/io/pebbletemplates/pebble/attributes/AttributeResolver.java

@@ -3,8 +3,25 @@
 import io.pebbletemplates.pebble.node.ArgumentsNode;
 import io.pebbletemplates.pebble.template.EvaluationContextImpl;
 
+/**
+ * Resolves instance attributes
+ */
 public interface AttributeResolver {
 
+  /**
+   * Attempts to resolve an attribute of the given instance. If this method returns {@code null},
+   * Pebble asks the next attribute resolver in the list.
+   *
+   * @param instance The object which is being accessed
+   * @param attributeNameValue The name of the attribute to resolve
+   * @param argumentValues fully evaluated positional arguments
+   * @param args The arguments
+   * @param context The evaluation context
+   * @param filename Filename of the template
+   * @param lineNumber the line number on which the expression is defined on.
+   * @return a {@link ResolvedAttribute} wrapping the attribute value, or {@code null} if the
+   * attribute could not be resolved
+   */
   ResolvedAttribute resolve(Object instance,
       Object attributeNameValue,
       Object[] argumentValues,

pebble/src/main/java/io/pebbletemplates/pebble/loader/Loader.java

@@ -25,7 +25,7 @@ public interface Loader<T> {
    * The reader which will be used by Pebble to read the contents of the template.
    *
    * @param cacheKey the cache key to use to load create the reader.
-   * @return A reader object
+   * @return A reader object, or {@code null} if the template does not exist
    */
   Reader getReader(T cacheKey);