Add an estimator for end frequency of the any custom waveform model (#…

…4911)

* added files

* addressed codeclimate issues

pycbc/waveform/plugin.py

@@ -75,6 +75,24 @@ def add_length_estimator(approximant, function):
     td_fd_waveform_transform(approximant)
 
 
+def add_end_frequency_estimator(approximant, function):
+    """ Add end frequency estimator for an approximant
+
+    Parameters
+    ----------
+    approximant : str
+        Name of approximant
+    function : function
+        A function which takes kwargs and returns the waveform end frequency
+    """
+    from pycbc.waveform.waveform import _filter_ends
+    if approximant in _filter_ends:
+        raise RuntimeError("Can't load freqeuncy estimator {}, the name is"
+                           " already in use.".format(approximant))
+
+    _filter_ends[approximant] = function
+
+
 def retrieve_waveform_plugins():
     """ Process external waveform plugins
     """
@@ -106,3 +124,7 @@ def retrieve_waveform_plugins():
     # Check for waveform length estimates
     for plugin in pkg_resources.iter_entry_points('pycbc.waveform.length'):
         add_length_estimator(plugin.name, plugin.resolve())
+
+    # Check for waveform end frequency estimates
+    for plugin in pkg_resources.iter_entry_points('pycbc.waveform.end_freq'):
+        add_end_frequency_estimator(plugin.name, plugin.resolve())