Close files after opening them

Using open() as context manager is the preferred way to close files to
guarantee exception safety. This commit solves an occasional
ResourceWarning, when CylP is used in unit tests run by pytest. There
are more direct calls of open() without context manager in setup.py.

cylp/__init__.py

@@ -1,4 +1,5 @@
 import os
 from os.path import realpath, join
 currentDir = os.path.dirname(realpath(__file__))
-__version__ = open(join(currentDir, 'VERSION')).read().strip()
+with open(join(currentDir, 'VERSION')) as f:
+    __version__ = f.read().strip()

cylp/py/QP/QP.py

@@ -1259,15 +1259,14 @@ def Wolfe(self, method='w'):
         qobj = 0.5 * x.T * G * x + np.dot(c, x) - self.objectiveOffset
 
         print(s.iteration)
-        f = open('qpout', 'a')
-        st = '%s %s %s %s %s %s %s\n' % (self.filename.ljust(30), method.ljust(2),
+        with open('qpout', 'a') as f:
+            st = '%s %s %s %s %s %s %s\n' % (self.filename.ljust(30), method.ljust(2),
                 str(round(s.objectiveValue, 5)).ljust(8),
                 str(round(qobj, 5)).ljust(8),
                 str(timeToMake),
                 str(timeToSolve),
                 str(timeToMake + timeToSolve))
-        f.write(st)
-        f.close()
+            f.write(st)
 
 #        print(checkComp(s.primalVariableSolution['k1'],
 #                        s.primalVariableSolution['zk1']))