Remove Cython dependency and add numba instead

Cython was very problematic regarding packaging because we needed numpy
installed before cython build was called (to get includes with
np.get_includes()), but that was ether not possible automatically or might be
possible only with hacks.

Author: darcamo

build.py

@@ -1,54 +1,25 @@
-# from distutils.command.build_ext import build_ext
-# from distutils.errors import CCompilerError, DistutilsExecError, DistutilsPlatformError
-# from setuptools import Extension
-import numpy as np
-
-# ext_modules = [
-#     Extension(name="pyphysim.c_extensions.misc_c",
-#               sources=["pyphysim/util/misc_c.pyx"],
-#               include_dirs=[np.get_include()]),
-# ]
-
-# class BuildFailed(Exception):
-#     pass
-
-# class ExtBuilder(build_ext):
-#     def run(self):
-#         try:
-#             build_ext.run(self)
-#         except (DistutilsPlatformError, FileNotFoundError):
-#             raise BuildFailed('File not found. Could not compile C extension.')
-
-#     def build_extension(self, ext):
-#         try:
-#             build_ext.build_extension(self, ext)
-#         except (CCompilerError, DistutilsExecError, DistutilsPlatformError,
-#                 ValueError):
-#             raise BuildFailed('Could not compile C extension.')
-
-# def build(setup_kwargs):
-#     """
-#     This function is mandatory in order to build the extensions.
-#     """
-#     setup_kwargs.update({
-#         "ext_modules": ext_modules,
-#         "cmdclass": {
-#             "build_ext": ExtBuilder
-#         }
-#     })
-
 from setuptools import Extension
-from Cython.Build import cythonize
-
-cyfuncs_ext = Extension(name="pyphysim.c_extensions.misc_c",
-                        sources=["pyphysim/util/misc_c.pyx"],
-                        include_dirs=[np.get_include()])
-
-EXTENSIONS = [cyfuncs_ext]
 
 
 def build(setup_kwargs):
-    setup_kwargs.update({
-        'ext_modules': cythonize(EXTENSIONS, language_level=3),
-        'zip_safe': False,
-    })
+    try:
+        import numpy as np
+        from Cython.Build import cythonize
+
+        cyfuncs_ext = Extension(name="pyphysim.c_extensions.misc_c",
+                                sources=["pyphysim/util/misc_c.pyx"],
+                                include_dirs=[np.get_include()])
+
+        EXTENSIONS = [cyfuncs_ext]
+
+        setup_kwargs.update({
+            'ext_modules':
+            cythonize(EXTENSIONS, language_level=3),
+            'zip_safe':
+            False,
+        })
+    except ModuleNotFoundError:
+        import warnings
+        warnings.warn(
+            "numpy and cython must be installed to compyle cython extensions in pyphysim"
+        )