Fixing the type system for datagrid types

[brainandforce]

RealSpaceDataGrid and HKLData should have subtyped AbstractArray to begin with. I've done this and simplified a vast number of the method definitions. Both these types now subtypes now subtype AbstractDataGrid which itself subtypes AbstractArray, so a good number of methods that arrays should have are already defined.

In practice, this may not break anything, but the relationships betwen the types is different. Also, AbstractCrystalData, AbstractRealSpaceData, and AbstractReciprocalSpaceData are now gone, as they served no real purpose. So has grid() - now convert(::Type{<:Array}, ::AbstractDataGrid) is defined.

I don't think linear indexing is needed for these types, just with the internals.

[brainandforce]

I think I need to update the generation of documentation as well...leaving this here for future me

[codecov[bot]]

Codecov Report

Patch coverage: 29.85% and project coverage change: +0.01 :tada:

Comparison is base (cb931ab) 30.79% compared to head (597ee25) 30.80%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #148 +/- ## ========================================== + Coverage 30.79% 30.80% +0.01% ========================================== Files 16 18 +2 Lines 1429 1396 -33 ========================================== - Hits 440 430 -10 + Misses 989 966 -23 ``` | [Impacted Files](https://codecov.io/gh/brainandforce/Electrum.jl/pull/148?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://codecov.io/gh/brainandforce/Electrum.jl/pull/148?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brandon+Flores#diff-c3JjL0VsZWN0cnVtLmps) | `0.00% <ø> (ø)` | | | [src/types.jl](https://codecov.io/gh/brainandforce/Electrum.jl/pull/148?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brandon+Flores#diff-c3JjL3R5cGVzLmps) | `0.00% <0.00%> (ø)` | | | [src/software/abinit.jl](https://codecov.io/gh/brainandforce/Electrum.jl/pull/148?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brandon+Flores#diff-c3JjL3NvZnR3YXJlL2FiaW5pdC5qbA==) | `45.75% <8.33%> (ø)` | | | [src/data/reciprocalspace.jl](https://codecov.io/gh/brainandforce/Electrum.jl/pull/148?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brandon+Flores#diff-c3JjL2RhdGEvcmVjaXByb2NhbHNwYWNlLmps) | `10.52% <20.00%> (-1.69%)` | :arrow_down: | | [src/data/realspace.jl](https://codecov.io/gh/brainandforce/Electrum.jl/pull/148?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brandon+Flores#diff-c3JjL2RhdGEvcmVhbHNwYWNlLmps) | `27.77% <25.00%> (-2.78%)` | :arrow_down: | | [src/lattices.jl](https://codecov.io/gh/brainandforce/Electrum.jl/pull/148?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brandon+Flores#diff-c3JjL2xhdHRpY2VzLmps) | `62.26% <33.33%> (-1.20%)` | :arrow_down: | | [src/data/grids.jl](https://codecov.io/gh/brainandforce/Electrum.jl/pull/148?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brandon+Flores#diff-c3JjL2RhdGEvZ3JpZHMuamw=) | `42.10% <42.10%> (ø)` | | | [src/filetypes.jl](https://codecov.io/gh/brainandforce/Electrum.jl/pull/148?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brandon+Flores#diff-c3JjL2ZpbGV0eXBlcy5qbA==) | `41.47% <50.00%> (ø)` | | | [src/data/fft.jl](https://codecov.io/gh/brainandforce/Electrum.jl/pull/148?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brandon+Flores#diff-c3JjL2RhdGEvZmZ0Lmps) | `50.00% <100.00%> (-16.67%)` | :arrow_down: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brandon+Flores). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Brandon+Flores)

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