Replace F77 efermi with pure python efermi

Build fortran code bring some unconvinients to package maintainance such
as failed in building docs in readthedocs since the docker image of
readthedocs contain no fortran compiler, and the problem of wired
setup.py setting to build and install the package.

I copy and paste the pure python efermi code from Austin to the package.
The performence not a big concern in this sssp-workflow, because it only
used in calculating the fermi level for metals and fermi level with
specific energy level shifts.

.gitignore

@@ -1,7 +1,6 @@
 *.pyc
 *.swo
 *.swp
-efermi_module*
 ~*
 *~
 *.pdf

.pre-commit-config.yaml

@@ -44,6 +44,9 @@ repos:
         language: system
         exclude: &exclude_files >
             (?x)^(
+                aiida_sssp_workflow/workflows/convergence/.*|
+                efermi/efermi.py|
+                aiida_sssp_workflow/helpers.py|
                 setup.py|
                 examples/.*|
                 docs/.*|

aiida_sssp_workflow/calculations/calculate_bands_distance.py

@@ -10,13 +10,13 @@
 
 @calcfunction
 def calculate_bands_distance(bands_structure_a: orm.BandsData,
-                             band_parameters_a: orm.Dict,
+                             bands_parameters_a: orm.Dict,
                              bands_structure_b: orm.BandsData,
-                             band_parameters_b: orm.Dict, smearing: orm.Float,
+                             bands_parameters_b: orm.Dict, smearing: orm.Float,
                              is_metal: orm.Bool):
     """doc"""
     res = get_bands_distance(bands_structure_a, bands_structure_b,
-                             band_parameters_a, band_parameters_b,
+                             bands_parameters_a, bands_parameters_b,
                              smearing.value, is_metal.value)
 
     return orm.Dict(
@@ -59,11 +59,9 @@ def fermi_dirac(band_energy, fermi_energy, smearing):
 def retrieve_bands(bandsdata: orm.BandsData, start_band, num_electrons, efermi,
                    smearing, is_metal):
     """
-    :bandsdata:
-    ...
-    TODO docstring
+    docstring
     """
-    from sssp.efermi_module import efermi as efermi_calc  # pylint: disable=no-name-in-module, import-error
+    from efermi import pyefermi
 
     bands = bandsdata.get_bands()
     bands = bands - efermi  # shift all bands to fermi energy 0
@@ -75,14 +73,13 @@ def retrieve_bands(bandsdata: orm.BandsData, start_band, num_electrons, efermi,
     if is_metal:
         nelectrons = num_electrons
         nkpoints = np.shape(bands)[0]
-        nbands = np.shape(bands)[1]
         weights = np.ones(nkpoints) / nkpoints
         bands = np.asfortranarray(bands)
+        meth = 2  # firmi-dirac smearing
+
+        output_efermi = pyefermi(bands, weights, nelectrons, smearing,
+                                 nkpoints, meth)
 
-        # 2 for firmi-dirac smearing
-        res = efermi_calc(nelectrons, nbands, smearing, nkpoints, weights, 0.0,
-                          bands, 2)
-        output_efermi = res[1]
     else:
         homo_energy = get_homo(bands, num_electrons)
         output_efermi = homo_energy