Small javadoc update, and add license headers for a few files

Author: jhalterman

src/main/java/dev/failsafe/Failsafe.java

@@ -28,9 +28,9 @@
  */
 public class Failsafe {
   /**
-   * Creates and returns a new {@link FailsafeExecutor} instance that will handle failures according to the given
-   * policies. The policies are composed around an execution and will handle execution results in reverse, with the last
-   * policy being applied first. For example, consider:
+   * Creates and returns a new {@link FailsafeExecutor} instance that will handle failures according to the given {@code
+   * outerPolicy} and {@code policies}. The policies are composed around an execution and will handle execution results
+   * in reverse, with the last policy being applied first. For example, consider:
    * <p>
    * <pre>
    *   Failsafe.with(fallback, retryPolicy, circuitBreaker).get(supplier);

src/main/java/dev/failsafe/internal/util/Lists.java

@@ -1,3 +1,18 @@
+/*
+ * Copyright 2011-2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License
+ */
 package dev.failsafe.internal.util;
 
 import java.util.ArrayList;

src/main/java/dev/failsafe/internal/util/Maths.java

@@ -1,3 +1,18 @@
+/*
+ * Copyright 2011-2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License
+ */
 package dev.failsafe.internal.util;
 
 /**