don't broadcast in issubset

[jishnub]

This makes the code cleaner as well, aside from not materializing the array, and allows short-circuiting. Also, fix some docstrings.

[codecov[bot]]

Codecov Report

Base: 86.09% // Head: 85.83% // Decreases project coverage by -0.26% :warning:

Coverage data is based on head (373184f) compared to base (8bce5e6). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #126 +/- ## ========================================== - Coverage 86.09% 85.83% -0.27% ========================================== Files 31 31 Lines 2496 2626 +130 ========================================== + Hits 2149 2254 +105 - Misses 347 372 +25 ``` | [Impacted Files](https://codecov.io/gh/JuliaApproximation/DomainSets.jl/pull/126?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation) | Coverage Δ | | |---|---|---| | [src/generic/setoperations.jl](https://codecov.io/gh/JuliaApproximation/DomainSets.jl/pull/126/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL2dlbmVyaWMvc2V0b3BlcmF0aW9ucy5qbA==) | `92.21% <100.00%> (-0.60%)` | :arrow_down: | | [src/domains/interval.jl](https://codecov.io/gh/JuliaApproximation/DomainSets.jl/pull/126/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL2RvbWFpbnMvaW50ZXJ2YWwuamw=) | `88.81% <0.00%> (-5.84%)` | :arrow_down: | | [src/domains/point.jl](https://codecov.io/gh/JuliaApproximation/DomainSets.jl/pull/126/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL2RvbWFpbnMvcG9pbnQuamw=) | `100.00% <0.00%> (ø)` | | | [src/generic/lazy.jl](https://codecov.io/gh/JuliaApproximation/DomainSets.jl/pull/126/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL2dlbmVyaWMvbGF6eS5qbA==) | `84.31% <0.00%> (+0.31%)` | :arrow_up: | | [src/generic/domain.jl](https://codecov.io/gh/JuliaApproximation/DomainSets.jl/pull/126/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JuliaApproximation#diff-c3JjL2dlbmVyaWMvZG9tYWluLmps) | `93.65% <0.00%> (+1.71%)` | :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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[daanhb]

Looks good to me, thanks