Usability improvements

- Preserve indentation when a line starts with a delimiter
  - Useful for aligning multi-line method chains
- Renamed `margin_{left,right}` to `{left,right}_margin
  - Makes it easier to type in (`l`, `r`)
  - `margin_{left,right}` is still supported
- Margins can be specified as the number of spaces, or as an arbitrary string

test/basic.md

@@ -84,3 +84,26 @@ aa >= bb
 aaaaa /* bbbbb */      == ccccc /* != eeeee = */ === fffff
 
 ```
+
+my_object
+      .method1.chain
+    .second_method.call
+      .third.call
+     .method_4.execute
+
+my_object.
+      method1.chain.
+    second_method.call.
+      third.call.
+     method_4.execute
+
+   | Option| Type | Default | Description |
+    |--|--|--|--|
+       | threads | Fixnum | 1 | number of threads in the thread pool |
+  |queues |Fixnum | 1 | number of concurrent queues |
+   |queue_size | Fixnum | 1000 | size of each queue |
+    |   interval | Numeric | 0 | dispatcher interval for batch processing |
+       |batch | Boolean | false | enables batch processing mode |
+   |batch_size | Fixnum | nil | number of maximum items to be assigned at once |
+   |logger | Logger | nil | logger instance for debug logs |
+