Mark `ephem.py` as deprecated

I just spent twenty minutes trying to figure out why there are two
duplicate implementations of Chebyshev before finally reconstructing
why.  So let’s mark all of these routines as clearly deprecated, so in
the future I remember it each time I enter the file!

jplephem/ephem.py

@@ -1,5 +1,14 @@
-"""Compute positions from an ephemeris installed as a Python package."""
+"""Compute positions from an ephemeris installed as a Python package.
 
+Note: This entire module is DEPRECATED.  The idea of distributing JPL
+ephemerides as Python packages proved to be impractical (they were much
+too large for the Python Package Index to easily store and distribute),
+and it forced `jplephem` users get their ephemerides from a different
+source than mainline astronomers, who use SPICE files.  This package's
+documentation now recommends avoiding this old code, and using the
+features now build directly into the `SPK` class instead.
+
+"""
 import os
 import numpy as np
 
@@ -9,7 +18,7 @@ class DateError(ValueError):
 
 
 class Ephemeris(object):
-    """A JPL planetary ephemeris that, given dates, computes positions."""
+    """[DEPRECATED] JPL planetary ephemeris for computing positions on dates."""
 
     def __init__(self, module):
         self.name = module.__name__.upper()
@@ -26,18 +35,18 @@ class Ephemeris(object):
         self.sets = {}
 
     def path(self, filename):
-        """Compute the path to a particular file in the ephemeris."""
+        """[DEPRECATED] Compute the path to a particular file in the ephemeris."""
         return os.path.join(self.dirpath, filename)
 
     def load(self, name):
-        """Load the polynomial series for `name` and return it."""
+        """[DEPRECATED] Load the polynomial series for `name` and return it."""
         s = self.sets.get(name)
         if s is None:
             self.sets[name] = s = np.load(self.path('jpl-%s.npy' % name))
         return s
 
     def position(self, name, tdb, tdb2=0.0):
-        """Compute the position of `name` at time ``tdb [+ tdb2]``.
+        """[DEPRECATED] Compute the position of `name` at time ``tdb [+ tdb2]``.
 
         The position is returned as a NumPy array ``[x y z]``.
 
@@ -59,7 +68,7 @@ class Ephemeris(object):
         return self.position_from_bundle(bundle)
 
     def position_and_velocity(self, name, tdb, tdb2=0.0):
-        """Compute the position and velocity of `name` at ``tdb [+ tdb2]``.
+        """[DEPRECATED] Compute the position and velocity of `name` at ``tdb [+ tdb2]``.
 
         The position and velocity are returned in a 2-tuple::
 
@@ -85,7 +94,7 @@ class Ephemeris(object):
         return position, velocity
 
     def compute(self, name, tdb):
-        """Legacy routine that concatenates position and velocity vectors.
+        """[DEPRECATED] Legacy routine that concatenates position and velocity vectors.
 
         This routine is deprecated.  Use the methods `position()` and
         `position_and_velocity()` instead.  This method follows the same
@@ -101,7 +110,7 @@ class Ephemeris(object):
         return np.concatenate((position, velocity))
 
     def compute_bundle(self, name, tdb, tdb2=0.0):
-        """Return a tuple of coefficients and parameters for `tdb`.
+        """[DEPRECATED] Return a tuple of coefficients and parameters for `tdb`.
 
         The return value is a tuple that bundles together the
         coefficients and other Chebyshev intermediate values that are
@@ -162,13 +171,13 @@ class Ephemeris(object):
         return bundle
 
     def position_from_bundle(self, bundle):
-        """Return position, given the `coefficient_bundle()` return value."""
+        """[DEPRECATED] Return position, given the `coefficient_bundle()` return value."""
 
         coefficients, days_per_set, T, twot1 = bundle
         return (T.T * coefficients).sum(axis=2)
 
     def velocity_from_bundle(self, bundle):
-        """Return velocity, given the `coefficient_bundle()` return value."""
+        """[DEPRECATED] Return velocity, given the `coefficient_bundle()` return value."""
 
         coefficients, days_per_set, T, twot1 = bundle
         coefficient_count = coefficients.shape[2]