Refactor the Composition type constructors

[eliascarv]

master:

julia> Random.seed!(2);

julia> inds = shuffle(1:100_000);

julia> coda = CoDaArray((a = rand(100_000), b = rand(100_000), c = rand(100_000)));

julia> @btime coda[inds];
  5.380 s (4299492 allocations: 161.74 MiB)

This PR:

julia> Random.seed!(2);

julia> inds = shuffle(1:100_000);

julia> coda = CoDaArray((a = rand(100_000), b = rand(100_000), c = rand(100_000)));

julia> @btime coda[inds];
  18.994 ms (500002 allocations: 18.31 MiB)

[codecov-commenter]

Codecov Report

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

Comparison is base (d49daf5) 84.71% compared to head (9d2d580) 84.91%.

Files	Patch %	Lines
src/compositions.jl	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #42      +/-   ##
==========================================
+ Coverage   84.71%   84.91%   +0.19%     
==========================================
  Files           9        9              
  Lines         229      232       +3     
==========================================
+ Hits          194      197       +3     
  Misses         35       35              

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