Adding objectid filter docs (#173)

* Adding objectid filter docs

* Fixing some build issues

Author: jeff-allen-mongo

source/filter-documents.txt

@@ -44,7 +44,9 @@ options. You can filter fields with the following data types:
 
 - :ref:`Numeric <filter-numeric>`
 
-- :ref:`String <filter-string>`
+- :ref:`String <filter-string-objectid>`
+
+- :ref:`ObjectId <filter-string-objectid>`
 
 - :ref:`Date <filter-date>`
 
@@ -89,40 +91,48 @@ can filter based on minimum and/or maximum values for that field.
    Alternatively, if :guilabel:`Inclusive` is off, |charts| shows
    documents where the field is greater than ``5``.
 
-.. _filter-string:
+.. _filter-string-objectid:
 
-Filter String Fields
-~~~~~~~~~~~~~~~~~~~~
+Filter String and ObjectId Fields
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-When you drag a string field to the filter panel, |charts| displays a
-list of up to 20 distinct field values. If more than 20 distinct values
-exist, |charts| displays 20 randomly selected values.
+When you drag a string or
+:manual:`ObjectId </reference/bson-types/#objectid>` field to the filter
+panel, |charts| displays a list of up to 20 distinct field values. If
+more than 20 distinct values exist, |charts| displays 20 randomly
+selected values.
 
 The list also includes:
 
 - :guilabel:`NULL / MISSING` for documents with ``null`` values for
   the field or are missing the field.
 
-- :guilabel:`Empty String` for documents with ``""`` values for the
-  field.
+- :guilabel:`Empty String` for documents with
+  ``""`` values for the string field. (*String fields only.*)
 
-Select the string values to display in the chart. By default, all
+Select the values to display in the chart. By default, all
 values are selected.
 
 .. tip::
 
-   If all strings are selected, you can click :guilabel:`Deselect All` 
-   at the top of the list to hide all strings.
+   If all values are selected, you can click :guilabel:`Deselect All` 
+   at the top of the list to hide all values.
 
-   If not all strings are selected, you can click :guilabel:`Select All`
-   to return to the default state of having all strings displayed.
+   If not all values are selected, you can click :guilabel:`Select All`
+   to return to the default state of having all values displayed.
 
-Display Strings Not in the List
-```````````````````````````````
+Display Strings and ObjectIds Not in the List
+`````````````````````````````````````````````
 
 To display a specific value not included in the list, add the value by
 clicking :guilabel:`Add Value`.
 
+.. important::
+
+   For :manual:`ObjectId </reference/bson-types/#objectid>` fields,
+   value you input must be a well-formed ObjectId, or else
+   |charts| does not accept the value.
+
 To display *all* other values not included in the list, check
 :guilabel:`All other values`.