Rename Point3::isNull() and Vector3::isNull() to isZero()

This renames the Point3::isNull() and Vector3::isNull()
methods to isZero().

Author: kylelutz

src/chemkit/point3.pxd

@@ -45,4 +45,4 @@ cdef extern from "chemkit/point3.h" namespace "chemkit":
         double x()
         double y()
         double z()
-        bool isNull()
+        bool isZero()

src/chemkit/point3.pxi

@@ -63,7 +63,7 @@ cdef class Point3:
 
         return self._point3.z()
 
-    def isNull(self):
-        """Returns True if the point is null (i.e. (0, 0, 0))."""
+    def isZero(self):
+        """Returns True if the point is zero (i.e. (0, 0, 0))."""
 
-        return self._point3.isNull()
+        return self._point3.isZero()

src/chemkit/vector3.pxd

@@ -45,4 +45,4 @@ cdef extern from "chemkit/vector3.h" namespace "chemkit":
         double x()
         double y()
         double z()
-        bool isNull()
+        bool isZero()

src/chemkit/vector3.pxi

@@ -63,7 +63,7 @@ cdef class Vector3:
 
         return self._vector3.z()
 
-    def isNull(self):
-        """Returns True if the vector is null (i.e. (0, 0, 0))."""
+    def isZero(self):
+        """Returns True if the vector is zero (i.e. (0, 0, 0))."""
 
-        return self._vector3.isNull()
+        return self._vector3.isZero()