Change ShapedAsNT to not be a 0-dim array

[oschulz]

Also support InverseFunctions.jl and ChangesOfVariables.jl.

[codecov[bot]]

Codecov Report

Merging #52 (807d683) into master (3372750) will decrease coverage by 4.51%. The diff coverage is 81.20%.

@@            Coverage Diff             @@
##           master      #52      +/-   ##
==========================================
- Coverage   92.93%   88.41%   -4.52%     
==========================================
  Files          13       12       -1     
  Lines         708      829     +121     
==========================================
+ Hits          658      733      +75     
- Misses         50       96      +46     

Impacted Files	Coverage Δ
src/value_accessor.jl	92.59% <33.33%> (-7.41%)	:arrow_down:
src/array_shape.jl	83.58% <50.00%> (-11.50%)	:arrow_down:
src/functions.jl	90.47% <50.00%> (-4.53%)	:arrow_down:
src/value_shape.jl	81.48% <76.92%> (-10.36%)	:arrow_down:
src/named_tuple_shape.jl	87.07% <81.42%> (-2.93%)	:arrow_down:
src/named_tuple_dist.jl	89.93% <84.61%> (-1.74%)	:arrow_down:
src/const_value_shape.jl	96.29% <90.00%> (-3.71%)	:arrow_down:
src/const_value_dist.jl	97.14% <100.00%> (ø)
src/distributions.jl	82.75% <100.00%> (-8.16%)	:arrow_down:
src/reshaped_dist.jl	100.00% <100.00%> (ø)
... and 7 more

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[oschulz]

CC @jknollm, @vindex10, @apmypb

This should fix our Zygote pullback problems, e.g. for MGVI.jl. Changing ShapedAsNT to not be a 0-dim array of NamedTuple allows for a cleaner approach in general, it also circumvents Zygote's special handling of arrays.

This also creates a clean separation between a NamedTuple and a ShapedAsNT (which now is mutable array-backed named-tuple-like type in it's own right). Users can now choose if they want distributions of NamedTuple or ShapedAsNT (with NamedTuple as the default).

This is breaking and will require some changes in BAT.jl to adapt to it - hopefully not too many, should be done soon.