docstr: Return precision/recall curve
code: def precision_recall_curve(self, label=None):
      """Return precision/recall curve"""
      if label:
          label_id = self.f.get_label_id(label)
          pair_list = self.m.precisionRecallCurveLabel(label_id)
      else:
          pair_list = self.m.precisionRecallCurve()
  
      if pair_list:
          precision, recall = zip(*pair_list)
      else:
          precision, recall = ([], ())
  
      return np.array(precision, copy=False), np.array(
          recall, copy=False
      )
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from __future__ import unicode_literals
  import fasttext_pybind
  import numpy
  import multiprocessing
  import sys
  from itertools import chain
label_desc: Use image node_id 3 for calling the _Meter obj's underlying member method code with example usage: obj.precision_recall_curve(label) and returns: np,  np