Convert sweep module and class to algorithm

Since an algorithm can use more than one sweep, the sweep class doesn't
fit very good as it is right now. For this reasen it got converted to a
more general class named algorithm, that shall be used as parent for
every individual algorithm. The exact behaviour of the algorithm is
then defined in the child classes.

algorithm.py

@@ -8,20 +8,18 @@ import copy
 import linesegment
 import point
 
-class Sweep():
+class Algorithm():
 
     "The Sweep class is the base class for each individual sweep algorithm"
 
     # pylint: disable=too-many-instance-attributes
 
     def __init__(self):
-        self._sss = None            # The sweep status structure
-        self._es = None             # The event structure
         self._input = None          # The input values
+        self._result = None         # The result of the sweep
         self._ready = False         # If the sweep is reade to be executed
         self._running = False       # If the sweep is currently running
         self._num_steps = {}        # The number of steps that were needed to solve the problem
-        self._result = None         # The result of the sweep
 
     def start(self):
         """Start the performing the algorithm. Return True if it was successful"""
@@ -30,8 +28,10 @@ class Sweep():
             return False
         self._running = True
         return True
+    def get_result(self):
+        return self._result
 
-class SweepNearestNeighbors(Sweep):
+class NearestNeighborsSweep(Algorithm):
 
     """Calculate the pair of points inside a set, that have the minimal distance between each
     other inside this set"""