Use IOBuffer in _inflate()

[kimikage]

I am not sure whether it is worth merging this PR, as I do not know how to use "test_performance.jl" properly.
This is just a conceptual example of what I see with issue #19.

In other words, I was interested in proper handling of the types, and I no longer care much for the performance improvements in this package.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.37%. Comparing base (f16eec8) to head (0533ce8).
Report is 2 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master      #22      +/-   ##
==========================================
+ Coverage   99.35%   99.37%   +0.01%     
==========================================
  Files           1        1              
  Lines         468      482      +14     
==========================================
+ Hits          465      479      +14     
  Misses          3        3              

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[GunnarFarneback]

The usual result is that you run test_performance.jl for a good while without and with some change, then you get back results which are inconclusive with some cases getting faster and some getting slower, which is what I'm seeing here as well.

I'm also not too enthusiastic about optimizing this code, but mostly because I know that if you port libdeflate to Julia, you get something which is not only faster than this code, but also faster than libz.

[GunnarFarneback]

Incidentally #9 also targets append! and would have solved half of the 32-bit issue.