refactor: reduce requirements, rm outDir before build.

[knightedcodemonkey]

• Use dist as a default outDir when one is not defined.
• rm the outDir prior to build.
• Add some timing around preparing parallel builds.
• Update README.

[codecov[bot]]

Codecov Report

Merging #11 (479693b) into main (78fa30b) will increase coverage by 0.01%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #11      +/-   ##
==========================================
+ Coverage   96.41%   96.42%   +0.01%     
==========================================
  Files           3        3              
  Lines         418      420       +2     
==========================================
+ Hits          403      405       +2     
  Misses         15       15              

Files Changed	Coverage Δ
src/duel.js	94.00% <100.00%> (+0.09%)	:arrow_up:
src/init.js	100.00% <100.00%> (ø)

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