add inverse transform for plotting

[codecov[bot]]

Codecov Report

Base: 38.52% // Head: 40.15% // Increases project coverage by +1.62% :tada:

Coverage data is based on head (9dae057) compared to base (6365bf7). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #63 +/- ## ========================================== + Coverage 38.52% 40.15% +1.62% ========================================== Files 11 11 Lines 1020 1046 +26 ========================================== + Hits 393 420 +27 + Misses 627 626 -1 ``` | [Impacted Files](https://codecov.io/gh/JuliaApproximation/AlgebraicCurveOrthogonalPolynomials.jl/pull/63?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation) | Coverage Δ | | |---|---|---| | [src/AlgebraicCurveOrthogonalPolynomials.jl](https://codecov.io/gh/JuliaApproximation/AlgebraicCurveOrthogonalPolynomials.jl/pull/63?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL0FsZ2VicmFpY0N1cnZlT3J0aG9nb25hbFBvbHlub21pYWxzLmps) | `74.46% <ø> (ø)` | | | [src/annulus.jl](https://codecov.io/gh/JuliaApproximation/AlgebraicCurveOrthogonalPolynomials.jl/pull/63?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL2FubnVsdXMuamw=) | `91.24% <100.00%> (+2.95%)` | :arrow_up: | 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=JuliaApproximation). 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=JuliaApproximation)

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[ioannisPApapadopoulos]

@dlfivefifty it passes the tests, ok to merge?

[ioannisPApapadopoulos]

Could we merge this? @dlfivefifty