Revise sections 'creating an index', 'index operations' and proofread 'create_index()' (#1896)

* small bugfix

* revise content of indexes.rst

* revise subsections in create_index.rst

* Apply suggestions from code review

Author: Onvember

doc/book/box/data_model.rst

@@ -386,7 +386,8 @@ Full information is in section
     | ``'string'``                   | :ref:`string <index-box_string>`          | TREE, BITSET or HASH                 |
     | (may also be called ``‘str’``) |                                           |                                      |
     +--------------------------------+-------------------------------------------+--------------------------------------+
-    | ``'varbinary'``                | :ref:`varbinary <index-box_bin>`          | TREE, BITSET or HASH                 |
+    | ``'varbinary'``                | :ref:`varbinary <index-box_bin>`          | TREE, HASH or BITSET                 |
+    |                                |                                           | (since version 2.7)                  |
     +--------------------------------+-------------------------------------------+--------------------------------------+
     | ``'uuid'``                     | :ref:`uuid <index-box_uuid>`              | TREE or HASH                         |
     +--------------------------------+-------------------------------------------+--------------------------------------+