Updating names of abinit file reading functions

[brainandforce]

Until now there were pairs of functions that did the same thing: read_abinit_density() and read_abinit_DEN(), read_abinit_potential() and read_abinit_POT(), and read_abinit_wavefunction() and read_abinit_WFK().

My future design plan is to have functions like read_abinit_density() return only the associated datagrid, and read_abinit_DEN() return the datagrid as part of a CrystalWithDatasets (or perhaps a similar future type that replaces it). So the aliasing of function names is being dropped.

@xamberl I'm going to loop you in on this

[codecov[bot]]

Codecov Report

Patch coverage: 66.66% and no project coverage change.

Comparison is base (d90478b) 49.10% compared to head (6a955b3) 49.10%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #161 +/- ## ======================================= Coverage 49.10% 49.10% ======================================= Files 17 17 Lines 1334 1334 ======================================= Hits 655 655 Misses 679 679 ``` | [Impacted Files](https://app.codecov.io/gh/brainandforce/Electrum.jl/pull/161?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brandon+Flores) | Coverage Δ | | |---|---|---| | [src/Electrum.jl](https://app.codecov.io/gh/brainandforce/Electrum.jl/pull/161?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brandon+Flores#diff-c3JjL0VsZWN0cnVtLmps) | `66.66% <ø> (ø)` | | | [src/software/abinit.jl](https://app.codecov.io/gh/brainandforce/Electrum.jl/pull/161?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brandon+Flores#diff-c3JjL3NvZnR3YXJlL2FiaW5pdC5qbA==) | `43.90% <66.66%> (ø)` | |

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.