Sync internal ecCodes bindings to eccodes-python

[alexamici]

This has been done to get ready to depend on the external binding in https://github.com/ecmwf/eccodes-python

Most of the work has been to move the API from bytes to str.

Versions 0.9.6.x will stay on the old internal API only. Starting form version 0.9.7 cfgrib can use the external bindings if installed.

[alexamici]

Done in branch stable/0.9.7.x

[datarods-svc]

@alexamici If this is so, then why does python -m cfgrib selfcheck fail? Due to this, I'm effectively still forced to use conda. Thanks.

Log:

(venv) (ingest-grib) AB-MacBook-Pro:ingest-grib ab$ python -V
Python 3.7.4

(venv) (ingest-grib) AB-MacBook-Pro:ingest-grib ab$ pip list
Package        Version
-------------- -------
attrs          19.1.0 
cffi           1.12.3 
cfgrib         0.9.7.1
Click          7.0    
eccodes-python 0.9.2  
numpy          1.17.0 
pip            19.2.2 
pycparser      2.19   
setuptools     40.8.0 

(venv) (ingest-grib) AB-MacBook-Pro:ingest-grib ab$ python -m cfgrib selfcheck
Traceback (most recent call last):
  File "/Users/ab/PycharmProjects/ingest-grib/venv/lib/python3.7/site-packages/cfgrib/bindings.py", line 48, in <module>
    lib = ffi.dlopen(libname)
  File "/Users/ab/PycharmProjects/ingest-grib/venv/lib/python3.7/site-packages/cffi/api.py", line 146, in dlopen
    lib, function_cache = _make_ffi_library(self, name, flags)
  File "/Users/ab/PycharmProjects/ingest-grib/venv/lib/python3.7/site-packages/cffi/api.py", line 828, in _make_ffi_library
    backendlib = _load_backend_lib(backend, libname, flags)
  File "/Users/ab/PycharmProjects/ingest-grib/venv/lib/python3.7/site-packages/cffi/api.py", line 823, in _load_backend_lib
    raise OSError(msg)
OSError: ctypes.util.find_library() did not manage to locate a library called 'libeccodes'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/runpy.py", line 183, in _run_module_as_main
    mod_name, mod_spec, code = _get_module_details(mod_name, _Error)
  File "/usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/runpy.py", line 142, in _get_module_details
    return _get_module_details(pkg_main_name, error)
  File "/usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/runpy.py", line 109, in _get_module_details
    __import__(pkg_name)
  File "/Users/ab/PycharmProjects/ingest-grib/venv/lib/python3.7/site-packages/cfgrib/__init__.py", line 19, in <module>
    from .cfmessage import CfMessage
  File "/Users/ab/PycharmProjects/ingest-grib/venv/lib/python3.7/site-packages/cfgrib/cfmessage.py", line 28, in <module>
    from . import messages
  File "/Users/ab/PycharmProjects/ingest-grib/venv/lib/python3.7/site-packages/cfgrib/messages.py", line 36, in <module>
    from . import bindings as eccodes
  File "/Users/ab/PycharmProjects/ingest-grib/venv/lib/python3.7/site-packages/cfgrib/bindings.py", line 86, in <module>
    CODES_TYPE_UNDEFINED = lib.GRIB_TYPE_UNDEFINED
  File "/Users/ab/PycharmProjects/ingest-grib/venv/lib/python3.7/site-packages/cfgrib/bindings.py", line 43, in __getattr__
    raise RuntimeError(self.message) from self.exc
RuntimeError: ecCodes library not found on the system.