Evaluate Fun{<:PointSpace} using a Point

[jishnub]

Since a Point may be converted to a Number, we may allow evaluating a Fun{<:PointSpace} at a point as well, so that the following works now:

julia> f = Fun(PointSpace(1:3))
Fun(PointSpace([1, 2, 3]), [1, 2, 3])

julia> f(Point(1))
1

[codecov[bot]]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (768625d) 75.07% compared to head (eb4f043) 75.18%. Report is 3 commits behind head on master.

Files	Patch %	Lines
src/Spaces/DiracSpace.jl	85.71%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #633 +/- ## ========================================== + Coverage 75.07% 75.18% +0.10% ========================================== Files 80 79 -1 Lines 8439 8439 ========================================== + Hits 6336 6345 +9 + Misses 2103 2094 -9 ```

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