Add a spinner for long running commands

[KristofferC]

Fixes #318

[codecov]

Codecov Report

Merging #607 (6b04ca2) into master (ea6fb75) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #607      +/-   ##
==========================================
+ Coverage   88.64%   88.66%   +0.02%     
==========================================
  Files           2        2              
  Lines         449      450       +1     
==========================================
+ Hits          398      399       +1     
  Misses         51       51              

Impacted Files	Coverage Δ
src/PackageCompiler.jl	88.53% <100.00%> (+0.02%)	⬆️

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