Add open(), read() and write() functions

This is the combination of a few commits from #18, plus a few more
things.
See also #14.

pysoundfile.py

@@ -700,6 +700,74 @@ def write(self, data):
         self.seek(curr, SEEK_SET, 'w')
 
 
+def open(*args, **kwargs):
+    """Return a new SoundFile object.
+
+    Takes the same arguments as SoundFile.__init__().
+
+    """
+    return SoundFile(*args, **kwargs)
+
+
+def read(file, frames=-1, start=None, stop=None, **kwargs):
+    """Read a sound file and return its contents as NumPy array.
+
+    The number of frames to read can be specified with frames, the
+    position to start reading can be specified with start.
+    By default, the whole file is read from the beginning.
+    Alternatively, a range can be specified with start and stop.
+    Both start and stop accept negative indices to specify positions
+    relative to the end of the file.
+
+    The keyword arguments out, dtype, fill_value and always_2d are
+    forwarded to SoundFile.read().
+    All further arguments are forwarded to SoundFile.__init__().
+
+    """
+    from inspect import getargspec
+
+    if frames >= 0 and stop is not None:
+        raise RuntimeError("Only one of {frames, stop} may be used")
+
+    read_kwargs = {}
+    for arg in getargspec(SoundFile.read).args:
+        if arg in kwargs:
+            read_kwargs[arg] = kwargs.pop(arg)
+    with SoundFile(file, 'r', **kwargs) as f:
+        start, stop, _ = slice(start, stop).indices(f.frames)
+        if stop < start:
+            stop = start
+        if frames < 0:
+            frames = stop - start
+        f.seek(start, SEEK_SET)
+        data = f.read(frames, **read_kwargs)
+    return data, f.sample_rate
+
+
+def write(data, file, sample_rate, *args, **kwargs):
+    """Write data from a NumPy array into a sound file.
+
+    If file exists, it will be overwritten!
+
+    If data is one-dimensional, a mono file is written.
+    For two-dimensional data, the columns are interpreted as channels.
+    All further arguments are forwarded to SoundFile.__init__().
+
+    Example usage:
+
+        import pysoundfile as sf
+        sf.write(myarray, 'myfile.wav', 44100, 'PCM_24')
+
+    """
+    data = _np.asarray(data)
+    if data.ndim == 1:
+        channels = 1
+    else:
+        channels = data.shape[1]
+    with SoundFile(file, 'w', sample_rate, channels, *args, **kwargs) as f:
+        f.write(data)
+
+
 def default_subtype(format):
     """Return default subtype for given format."""
     return _default_subtypes.get(str(format).upper())