Fixed no parameter changes when max_radii and cutoffs not used.

When any method in gradient generates parameter changes, these
are then run through gradient.check, which checks whether the radius
of unscaled parameter changes meets certain user specified conditions
(currently, those conditions are given in the __init__ statement of
gradient.Gradient).

It would first check for max_radii and then for cutoffs. However,
if neither were used, it would incorrectly return None rather than
returning the unscaled parameter changes.

This should fix issue #7.

gradient.py

@@ -79,10 +79,10 @@ def __init__(self,
             direc, ff, ff_lines, args_ff, args_ref)
         # Whether or not to generate parameters with these methods.
         self.do_lstsq = True
-        self.do_lagrange = False
-        self.do_levenberg = False
+        self.do_lagrange = True
+        self.do_levenberg = True
         self.do_newton = True
-        self.do_svd = False
+        self.do_svd = True
         # Particular settings for each method.
         # LEAST SQUARES
         self.lstsq_cutoffs = None
@@ -288,6 +288,8 @@ def check(changes, max_radii, cutoffs):
         elif cutoffs:
             if check_cutoffs(radius, cutoffs):
                 new_changes.append(change)
+        else:
+            new_changes.append(changes)
     return new_changes
 
 def check_cutoffs(par_rad, cutoffs):