message: Make pybind11 mandatory and simplify
  The use of install_requires and setup_requires looks strange, I would
  expect cython in setup_requires, not install_requires. But
  setup_requires doesn't seem to work so well anyway.
diff: @@ -12,6 +12,7 @@ from setuptools import setup, Extension
  from Cython.Build import cythonize
  from numpy import get_include as numpy_get_include
  import sys
  +import pybind11
  __author__ = "Vincent Rouvreau"
  __copyright__ = "Copyright (C) 2016 Inria"
  @@ -27,20 +28,6 @@ library_dirs=[@GUDHI_PYTHON_LIBRARY_DIRS@]
  include_dirs = [numpy_get_include(), '@CMAKE_CURRENT_SOURCE_DIR@/gudhi/', @GUDHI_PYTHON_INCLUDE_DIRS@]
  runtime_library_dirs=[@GUDHI_PYTHON_RUNTIME_LIBRARY_DIRS@]
  -# Copied from https://github.com/pybind/python_example/blob/master/setup.py
  -class get_pybind_include(object):
  - """Helper class to determine the pybind11 include path
  - The purpose of this class is to postpone importing pybind11
  - until it is actually installed, so that the ``get_include()``
  - method can be invoked. """
  -
  - def __init__(self, user=False):
  - self.user = user
  -
  - def __str__(self):
  - import pybind11
  - return pybind11.get_include(self.user)
  -
  # Create ext_modules list from module list
  ext_modules = []
  for module in modules:
  @@ -64,7 +51,7 @@ ext_modules.append(Extension(
  language = 'c++',
  include_dirs = include_dirs +
  ['@HERA_WASSERSTEIN_INCLUDE_DIR@',
  - get_pybind_include(False), get_pybind_include(True)],
  + pybind11.get_include(False), pybind11.get_include(True)],
  extra_compile_args=extra_compile_args + [@GUDHI_PYBIND11_EXTRA_COMPILE_ARGS@],
  ))
  @@ -76,6 +63,6 @@ setup(
  version='@GUDHI_VERSION@',
  url='http://gudhi.gforge.inria.fr/',
  ext_modules = ext_modules,
  - install_requires = ['cython','numpy >= 1.9','pybind11',],
  + install_requires = ['cython','numpy >= 1.9',],
  setup_requires = ['numpy >= 1.9','pybind11',],
  )
  