chore: replace multibase with multiformats

[achingbrain]

Swaps the multibase library for multiformats as it's much smaller.

[codecov-commenter]

Codecov Report

Merging #20 (aad6c6c) into master (744af83) will increase coverage by 0.32%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #20      +/-   ##
==========================================
+ Coverage   98.02%   98.35%   +0.32%     
==========================================
  Files           6        7       +1     
  Lines         203      243      +40     
  Branches       44       44              
==========================================
+ Hits          199      239      +40     
  Misses          4        4              

Impacted Files	Coverage Δ
from-string.js	100.00% <100.00%> (ø)
to-string.js	100.00% <100.00%> (ø)
util/bases.js	100.00% <100.00%> (ø)

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[achingbrain]

Needs multiformats/js-multiformats#102 to be resolved first.