Fix geometry example

Add missing functions for the geometry example

* docs/Geometry.rst - use from_regular rather than weird constructor
* pygorithm/geometry/polygon2.py - Add form-regular and alternate tuple
version for init

Author: Tjstretchalot

docs/Geometry.rst

@@ -14,7 +14,7 @@ Quick Start Guide
     from pygorithm.geometry import vector2
     
     # create a regular polygon
-    poly1 = polygon2.Polygon2(regular=True, sides=5, length=5)
+    poly1 = polygon2.Polygon2.from_regular(5, 5)
     
     # create a polygon from tuple (x, y) - note that the polygon must be concave
     poly2 = polygon2.Polygon2(points=[ (0, 0), (1, 0), (1, 1), (0, 1) ])

pygorithm/geometry/polygon2.py

@@ -62,7 +62,8 @@ def __init__(self, points, suppress_errors = False):
             suppressed.
         
         :param points: the ordered set of points on this polygon
-        :type points: list of :class:`pygorithm.geometry.vector2.Vector2`
+        :type points: list of :class:`pygorithm.geometry.vector2.Vector2` or \
+        list of (:class:`numbers.Number`, :class:`numbers.Number`)
         
         :param suppress_errors: True to not do somewhat expensive sanity checks
         :type suppress_errors: bool
@@ -74,6 +75,20 @@ def __init__(self, points, suppress_errors = False):
         """
         pass
 
+    @classmethod
+    def from_regular(cls, sides, length):
+        """
+        Create a new regular polygon.
+        
+        :param sides: the number of sides in the polygon
+        :type sides: :class:`numbers.Number`
+        :param length: the length of each sides
+        :type length: :class:`numbers.Number`
+        
+        :raises ValueError: if ``sides < 3`` or ``length <= 0``
+        """
+        pass
+        
     @property
     def area(self):
         """