docs: Add syncsets (#200)

* Mirror now has Synced HashSet and SortedSet

Documentation here:
https://vis2k.github.io/Mirror/Classes/SyncHashSet
https://vis2k.github.io/Mirror/Classes/SyncSortedSet

* Now both Mirror and MLAPI have sync sets

Author: paulpach

docs/_pages/features.html

@@ -183,6 +183,12 @@
                     <td><i class="fa fa-check" aria-hidden="true" style="color:green"></i></td>
                     <td><i class="fa fa-check" aria-hidden="true" style="color:green"></i></td>
                 </tr>
+                <tr>
+                    <td>SyncedSet</td>
+                    <td><i class="fa fa-check" aria-hidden="true" style="color:green"></i></td>
+                    <td><i class="fa fa-check" aria-hidden="true" style="color:green"></i></td>
+                    <td><i class="fa fa-times" aria-hidden="true" style="color:red"></i></td>
+                </tr>
                 <tr>
                     <td>SyncedDictionary</td>
                     <td><i class="fa fa-check" aria-hidden="true" style="color:green"></i></td>