Port to python 3

acquire.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 from __future__ import print_function
 import sys
 import os

imgstat.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 from __future__ import print_function
 import numpy as np
 from astropy.io import ascii

process.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 from __future__ import print_function
 import glob
 import numpy as np

stvid/satellite.py

@@ -47,7 +47,7 @@ def find_hough3d_lines(fname, ntrkmin=20, dr=8):
         return []
 
     # Clean output (a bit cluncky)
-    cleaned_output = output.replace("npoints=", "")
+    cleaned_output = output.decode("utf-8").replace("npoints=", "")
     cleaned_output = cleaned_output.replace(", a=(", " ")
     cleaned_output = cleaned_output.replace("), b=(", " ")
     cleaned_output = cleaned_output.replace(")", "")