go back to using a Vector for recycled frames

[KristofferC]

Before

julia> @time (p = @interpret(plot(rand(5))); @interpret(display(p)))
 12.059313 seconds (63.78 M allocations: 2.143 GiB, 2.58% gc time)

julia> @time (p = @interpret(plot(rand(5))); @interpret(display(p)))
 12.198480 seconds (65.08 M allocations: 2.175 GiB, 2.66% gc time)

After

julia> @time (p = @interpret(plot(rand(5))); @interpret(display(p)))
  9.768135 seconds (65.32 M allocations: 2.052 GiB, 2.97% gc time)

julia> @time (p = @interpret(plot(rand(5))); @interpret(display(p)))
  9.531303 seconds (64.33 M allocations: 2.011 GiB, 3.06% gc time)

[codecov-io]

Codecov Report

Merging #245 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #245      +/-   ##
==========================================
+ Coverage   87.13%   87.15%   +0.01%     
==========================================
  Files          14       14              
  Lines        1982     1985       +3     
==========================================
+ Hits         1727     1730       +3     
  Misses        255      255

Impacted Files	Coverage Δ
src/construct.jl	92.18% <100%> (+0.09%)	⬆️

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[timholy]

Nice! I am surprised our former troubles didn't rear up, but perhaps just emptying on initialization solved it? Anyway, very nice performance boost.