Add Github Actions workflow to build documentation (#993)

* Add workflow to build and check docs

* Fix docs build warnings

Author: alcaeus

source/reference/bson.txt

@@ -14,8 +14,8 @@ Overview
 --------
 
 MongoDB stores data records as BSON documents. BSON is a binary representation
-of :term:`JSON` documents, though it contains more data types than JSON. For the
-BSON spec, see `bsonspec.org <https://bsonspec.org/>`_.
+of JSON documents, though it contains more data types than JSON. For the BSON
+spec, see `bsonspec.org <https://bsonspec.org/>`_.
 
 By default, the |php-library| returns BSON documents as
 :phpclass:`MongoDB\\Model\\BSONDocument` objects and BSON arrays as
@@ -106,7 +106,7 @@ of the PHP class in a special property within the BSON document.
    When deserializing a PHP variable from BSON, the encoded class name of a
    :php:`Persistable <mongodb-bson-persistable>` object will override any class
    specified in the type map, but it will not override ``"array"`` and
-   ``"stdClass"`` or ``"object"``. This is discussed in the 
+   ``"stdClass"`` or ``"object"``. This is discussed in the
    :php:`persistence specification <mongodb.persistence>` but it bears
    repeating.
 
@@ -121,7 +121,7 @@ Consider the following class definition:
        private $id;
        private $name;
        private $createdAt;
-       
+
        public function __construct($name)
        {
            $this->id = new MongoDB\BSON\ObjectId;

source/reference/method/MongoDBChangeStream-current.txt

@@ -103,4 +103,4 @@ See Also
 - :ref:`Tailable Cursor Iteration <php-tailable-cursor>`
 - :manual:`Change Streams </changeStreams>` documentation in the MongoDB manual
 - :manual:`Change Events </reference/change-events/>` documentation in the
-  MongoDB manual
+  MongoDB manual

source/reference/method/MongoDBChangeStream-key.txt

@@ -73,4 +73,4 @@ See Also
 - :phpmethod:`MongoDB\\Database::watch()`
 - :php:`Iterator::key() <iterator.key>`
 - :ref:`Tailable Cursor Iteration <php-tailable-cursor>`
-- :manual:`Change Streams </changeStreams>` documentation in the MongoDB manual
+- :manual:`Change Streams </changeStreams>` documentation in the MongoDB manual