fix review remarks(doc, Makefile margins)

Author: stepan-neretin7

Diff for: Makefile

@@ -31,7 +31,7 @@ DATA_built  = $(RELEASE_SQL) \
 
 DOCS        = README.pg_sphere COPYRIGHT.pg_sphere
 REGRESS     = init tables points euler circle line ellipse poly path box index \
-              contains_ops contains_ops_compat bounding_box_gist gnomo epochprop\
+              contains_ops contains_ops_compat bounding_box_gist gnomo epochprop \
               spherepoint_array_center
 
 ifneq ($(USE_HEALPIX),0)

Diff for: doc/operators.sgm

@@ -393,8 +393,10 @@
                 The center operator <literal>@@</literal> is a non-boolean
                 unary operator returning the center of an object.  In the
                 current implementation of <application>pgSphere</application>,
-                only centers of circles, ellipses, point, array of points are supported. Instead
-                of using the operator, you can use the function
+                only centers of circles, ellipses, points, array of points are
+            </para>
+            <para>
+                supported. Instead of using the operator, you can use the function
                 <literal>center(object)</literal>.
             </para>
             <example>