Allow shorthand method for creating an option-less parser.

This is mostly just intended to make a simple filter example shorter.

src/filter.py

@@ -67,7 +67,7 @@ def get_stream_info(client, path):
 
 class Filter(object):
 
-    def __init__(self):
+    def __init__(self, parser_description = None):
         self._parser = None
         self._client_src = None
         self._client_dest = None
@@ -78,6 +78,9 @@ class Filter(object):
         self.end = None
         self.interhost = False
         self.force_metadata = False
+        if parser_description is not None:
+            self.setup_parser(parser_description)
+            self.parse_args()
 
     @property
     def client_src(self):

src/sinefit.py

@@ -157,7 +157,7 @@ def sfit4(data, fs):
     (Verified to match sfit4.m)
     """
     N = len(data)
-    t = linspace(0, (N-1) / fs, N)
+    t = linspace(0, (N-1) / float(fs), N)
 
     ## Estimate frequency using FFT (step b)
     Fc = fft(data)
@@ -182,7 +182,7 @@ def sfit4(data, fs):
     i = arccos((Z2*cos(ni2) - Z1*cos(ni1)) / (Z2-Z1)) / n
 
     # Convert to Hz
-    f0 = i * fs / N
+    f0 = i * float(fs) / N
 
     # Fit it.  We'll catch exceptions here and just returns zeros
     # if something fails with the least squares fit, etc.