mnt: fixed #477 and #478, changed *_current to *_transmission

The orbital_current was confusing for end-users as it
signalled it was a bias-window integrated quantity.

Now the routines have changed names and additional ones
have been added.

*_transmission: are the orbital/atom/... resolved
  transmissions (they have `E` as argument)
*_current: are the orbital/atom/... bias window
  integrated quantities that reflects the total
  current (they don't have `E` as argument)

This will break old users scripts as the interfaces
has also changed.
Now all electrode arguments defaults to the 1st electrode
and energy arguments are generally the first ones (except DOS).

This *should* be more what users want as for 2 electrode systems
they'll generally only calculate one orbital_current for the first
electrode.

For old users one can accommodate these settings by using this
small snippet:

if sisl.__version_tuple__[:3] >= (0, 13, 0):
   tbt.orbital_transmission(0.1, "Left")
else:
   tbt.orbital_current("Left", 0.1)

Same goes for the other equivalent routines.

CHANGELOG.md

@@ -5,7 +5,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html) once
 we hit release version 1.0.0.
 
-## [UNRELEASED] - YYYY-MM-DD
+## [0.13.0] - YYYY-MM-DD
 
 ### Added
 - enabled unit specification for lengths in cube-files
@@ -18,6 +18,19 @@ we hit release version 1.0.0.
 - orbital quantum numbers from HSX file was wrong in v1, #462
 - RealSpaceSI for right semi-infinite directions, #475
 
+### Changed
+- tbtncSileTBtrans and its derivates has changed, drastically.
+	This will accommodate changes related to #477 and #478.
+	Now `*_transmission` refers to energy resolved transmissions
+  and `*_current` reflects bias-window integrated quantities.
+	The defaults and argument order has changed drastically, so
+  users should adapt their scripts depending on `sisl` version.
+	A check can be made, `if sisl.__version_tuple__[:3] >= (0, 13, 0):`
+- To streamline argument order the `*_ACO[OH]P` routines have changed
+	`elec` and `E` argument order. This makes them compatible with
+	`orbital_transmission` etc.
+
+
 ## [0.12.2] - 2022-5-2
 
 ### Added

sisl/io/tbtrans/_cdf.py

@@ -17,6 +17,8 @@
 # Import the geometry object
 from sisl import Geometry, Atom, SuperCell
 from sisl.unit.siesta import unit_convert
+from sisl.physics.distribution import fermi_dirac
+
 
 __all__ = ['_ncSileTBtrans', '_devncSileTBtrans']
 
@@ -177,6 +179,41 @@ def Eindex(self, E):
                  f"{E:.5f} eV, found {ret_E:.5f} eV as the closest energy!")
         return idxE
 
+    def _bias_window_integrator(self, elec_from=0, elec_to=1):
+        r""" An integrator for the bias window between two electrodes
+
+        Given two chemical potentials this returns an integrator (function) which
+        returns weights for an input energy-point roughly equivalent to:
+
+        .. math::
+           dI = \mathrm dE\,[n_F(\mu_t, k_B T_t) - n_F(\mu_f, k_B T_f)]
+
+        In this case :mathrm:`\mathrm dE` is the distance between two consecutive
+        energy points in this file.
+
+        Parameters
+        ----------
+        elec_from: str, int
+           the originating electrode
+        elec_to: str, int
+           the absorbing electrode (different from `elec_from`)
+
+        """
+        elec_from = self._elec(elec_from)
+        kt_from = self.kT(elec_from)
+        mu_from = self.chemical_potential(elec_from)
+        elec_to = self._elec(elec_to)
+        kt_to = self.kT(elec_to)
+        mu_to = self.chemical_potential(elec_to)
+        # Get energies
+        E = self._E_T_sorted(elec_from, elec_to)[0]
+        dE = E[1] - E[0]
+
+        def integrator(E):
+            return dE * (fermi_dirac(E, kt_from, mu_from) - fermi_dirac(E, kt_to, mu_to))
+
+        return integrator
+
     def kindex(self, k):
         """ Return the index of the k-point that is closests to the queried k-point (in reduced coordinates)