Reindent auth rules section

RST expects sub lists to be indented by three or more spaces. By doing
so we can then rely on `#.` for automatic numbering.

specification/server_server_api.rst

@@ -359,7 +359,7 @@ The rules are as follows:
 1. If type is ``m.room.create``, allow if and only if it has no
    previous events - *i.e.* it is the first event in the room.
 
-2. If type is ``m.room.member``:
+#. If type is ``m.room.member``:
 
     a. If ``membership`` is ``join``:
 
@@ -375,7 +375,7 @@ The rules are as follows:
 
         #. Otherwise, reject.
 
-  b. If ``membership`` is ``invite``:
+    #. If ``membership`` is ``invite``:
 
         i. If the ``sender``'s current membership state is not ``join``, reject.
 
@@ -387,7 +387,7 @@ The rules are as follows:
 
         #. Otherwise, reject.
 
-  c. If ``membership`` is ``leave``:
+    #. If ``membership`` is ``leave``:
 
         i. If the ``sender`` matches ``state_key``, allow if and only if that user's
            current membership state is ``invite`` or ``join``.
@@ -403,7 +403,7 @@ The rules are as follows:
 
         #. Otherwise, reject.
 
-  d. If ``membership`` is ``ban``:
+    #. If ``membership`` is ``ban``:
 
         i. If the ``sender``'s current membership state is not ``join``, reject.
 
@@ -413,18 +413,18 @@ The rules are as follows:
 
         #. Otherwise, reject.
 
-  e. Otherwise, the membership is unknown. Reject.
+    #. Otherwise, the membership is unknown. Reject.
 
-3. If the ``sender``'s current membership state is not ``join``, reject.
+#. If the ``sender``'s current membership state is not ``join``, reject.
 
-4. If the event type's *required power level* is greater than the ``sender``'s power
+#. If the event type's *required power level* is greater than the ``sender``'s power
    level, reject.
 
-5. If type is ``m.room.power_levels``:
+#. If type is ``m.room.power_levels``:
 
     a. If there is no previous ``m.room.power_levels`` event in the room, allow.
 
-  b. For each of the keys ``users_default``, ``events_default``,
+    #. For each of the keys ``users_default``, ``events_default``,
        ``state_default``, ``ban``, ``redact``, ``kick``, ``invite``, as well as
        each entry being changed under the ``events`` or ``users`` keys:
 
@@ -434,15 +434,15 @@ The rules are as follows:
         #. If the new value is higher than the ``sender``'s current power level,
            reject.
 
-  c. For each entry being changed under the ``users`` key, other than the
+    #. For each entry being changed under the ``users`` key, other than the
        ``sender``'s own entry:
 
         i. If the current value is equal to the ``sender``'s current power level,
            reject.
 
-  d. Otherwise, allow.
+    #. Otherwise, allow.
 
-6. If type is ``m.room.redaction``:
+#. If type is ``m.room.redaction``:
 
     a. If the ``sender``'s power level is greater than or equal to the *redact
        level*, allow.
@@ -452,7 +452,7 @@ The rules are as follows:
 
     #. Otherwise, reject.
 
-7. Otherwise, allow.
+#. Otherwise, allow.
 
 .. NOTE::