Remove the unsupported optional limit argument

ReadableSearch has an optional limit argument
to limit the number of records streamed.

It is now the responsibility of the query
executor to enforce that limit.
Example added to the Readme

Author: hmalphettes

README.md

@@ -56,6 +56,25 @@ ws._write = function(chunk, enc, next) {
 rs.pipe(ws);
 ```
 
+If we want to start the stream at an offset and define a limit:
+
+```
+var offset = 7;
+var limit  = 21;
+var page   = 12;
+
+var searchExec = function searchExec(from, callback) {
+  client.search({
+    index: 'myindex',
+    from: from + offset,
+    size: (offset + from + page) > limit ? (limit - offset - from) : page,
+    body: {
+      query: { match_all: {} }
+    }
+  }, callback);
+};
+```
+
 ## Stream scroll/scan results from Elasticsearch
 ```
 var scrollExec = function scrollExec(from, callback) {

lib/readable-search.js

@@ -12,17 +12,13 @@ module.exports = ReadableHits;
 
 /**
  * @param queryExec an executable query functions that takes 2 arguments: the offset and a callback.
- * @param limit optional number of hits to stream
  */
-function ReadableHits(queryExec, limit) {
+function ReadableHits(queryExec) {
   Readable.call(this, {objectMode:true});
   this.queryExec = queryExec;
   this.total = -1;
   this.from = 0;
   this._next = true;
-  if (limit > 0) {
-    this.limit = limit;
-  }
 
 // current iteration through the page
   this._hits = [];