Merge pull request jashkenas#947 from lukeasrodgers/add_context_param…

…_to_docs

Updating docs with optional `context` arg for a few methods.

index.html

@@ -612,7 +612,7 @@ <h2 id="collections">Collection Functions (Arrays or Objects)</h2>
 </pre>
 
       <p id="groupBy">
-        <b class="header">groupBy</b><code>_.groupBy(list, iterator)</code>
+        <b class="header">groupBy</b><code>_.groupBy(list, iterator, [context])</code>
         <br />
         Splits a collection into sets, grouped by the result of running each
         value through <b>iterator</b>. If <b>iterator</b> is a string instead of
@@ -628,7 +628,7 @@ <h2 id="collections">Collection Functions (Arrays or Objects)</h2>
 </pre>
 
       <p id="countBy">
-        <b class="header">countBy</b><code>_.countBy(list, iterator)</code>
+        <b class="header">countBy</b><code>_.countBy(list, iterator, [context])</code>
         <br />
         Sorts a list into groups and returns a count for the number of objects
         in each group.
@@ -873,7 +873,7 @@ <h2 id="arrays">Array Functions</h2>
 </pre>
 
       <p id="sortedIndex">
-        <b class="header">sortedIndex</b><code>_.sortedIndex(list, value, [iterator])</code>
+        <b class="header">sortedIndex</b><code>_.sortedIndex(list, value, [iterator], [context])</code>
         <br />
         Uses a binary search to determine the index at which the <b>value</b>
         <i>should</i> be inserted into the <b>list</b> in order to maintain the <b>list</b>'s