Add Parker weighting for short scans

[JeffFessler]

Hopefully will address #39. Also using Type{<:Number} instead of DataType because somewhere the manual recommended it.

[codecov[bot]]

Codecov Report

Base: 99.61% // Head: 99.62% // Increases project coverage by +0.01% :tada:

Coverage data is based on head (1688f4c) compared to base (daecffe). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #40 +/- ## ========================================== + Coverage 99.61% 99.62% +0.01% ========================================== Files 31 31 Lines 774 797 +23 ========================================== + Hits 771 794 +23 Misses 3 3 ``` | [Impacted Files](https://codecov.io/gh/JuliaImageRecon/Sinograms.jl/pull/40?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None) | Coverage Δ | | |---|---|---| | [src/fbp/window.jl](https://codecov.io/gh/JuliaImageRecon/Sinograms.jl/pull/40/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-c3JjL2ZicC93aW5kb3cuamw=) | `100.00% <ø> (ø)` | | | [src/fbp2/back-fan.jl](https://codecov.io/gh/JuliaImageRecon/Sinograms.jl/pull/40/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-c3JjL2ZicDIvYmFjay1mYW4uamw=) | `97.95% <ø> (ø)` | | | [src/fbp2/back-par.jl](https://codecov.io/gh/JuliaImageRecon/Sinograms.jl/pull/40/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-c3JjL2ZicDIvYmFjay1wYXIuamw=) | `97.36% <ø> (ø)` | | | [src/fbp3/cbct-back.jl](https://codecov.io/gh/JuliaImageRecon/Sinograms.jl/pull/40/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-c3JjL2ZicDMvY2JjdC1iYWNrLmps) | `98.36% <ø> (ø)` | | | [src/geom/ct-geom.jl](https://codecov.io/gh/JuliaImageRecon/Sinograms.jl/pull/40/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-c3JjL2dlb20vY3QtZ2VvbS5qbA==) | `100.00% <ø> (ø)` | | | [src/geom/sino-geom.jl](https://codecov.io/gh/JuliaImageRecon/Sinograms.jl/pull/40/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-c3JjL2dlb20vc2luby1nZW9tLmps) | `100.00% <ø> (ø)` | | | [src/geom/util.jl](https://codecov.io/gh/JuliaImageRecon/Sinograms.jl/pull/40/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-c3JjL2dlb20vdXRpbC5qbA==) | `100.00% <ø> (ø)` | | | [src/fbp2/fbp.jl](https://codecov.io/gh/JuliaImageRecon/Sinograms.jl/pull/40/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-c3JjL2ZicDIvZmJwLmps) | `100.00% <100.00%> (ø)` | | | [src/fbp2/parker.jl](https://codecov.io/gh/JuliaImageRecon/Sinograms.jl/pull/40/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-c3JjL2ZicDIvcGFya2VyLmps) | `100.00% <100.00%> (ø)` | | | [src/fbp2/plan2.jl](https://codecov.io/gh/JuliaImageRecon/Sinograms.jl/pull/40/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None#diff-c3JjL2ZicDIvcGxhbjIuamw=) | `100.00% <100.00%> (ø)` | | | ... and [3 more](https://codecov.io/gh/JuliaImageRecon/Sinograms.jl/pull/40/diff?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=None) | | 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=None). 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=None)

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[tknopp]

Well, what should I say: It just works!

Thanks for the quick implementation!