Adds `Clone` trait to `ScaleLinear`.#9

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NatanFreeman wants to merge 5 commits intoaskanium:masterfrom

NatanFreeman:master

Commits on Jan 19, 2022

Implements copy trait for ScaleLinear.
Natan Freeman
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Adds ```Clone``` trait to ```ScaleLinear```.
Natan Freeman
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Commits on Jan 21, 2022

Sets ```x_scale``` to be public.
Natan Freeman
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Merge branch 'master' of https://github.com/NatanFreeman/rustplotlib
Natan Freeman
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Sets ```ScaleLinear``` privet fields to be public.
Natan Freeman
committed