Change three occurences of xrange() to range() for compatibility with…

[warrickball]

I just tried to run this basic example on my system under Python 3, which I called test_pymacula.py:

#!/usr/bin/env python3

import numpy as np
import matplotlib.pyplot as pl
import pymacula

t = np.arange(0, 500, 0.05)
model = pymacula.MaculaModel()
pl.plot(t, model(t))
pl.show()

and ran into the error

Traceback (most recent call last):
  File "test_pymacula.py", line 8, in <module>
    model = pymacula.MaculaModel()
  File "/home/wball/pypi/pymacula/pymacula/macula.py", line 179, in __init__
    self.spots = [Spot() for i in xrange(nspots)]
NameError: name 'xrange' is not defined

So I replaced three occurences of xrange to range. This gets the code running under Python 3. I haven't tested under Python 2 but as long as the number of spots is small I don't imagine there's a problem. If there is and you want to preserve Python 2 compatibility we can use a trick like

try:
    range = xrange
except NameError:
    pass

or something.