Implement memset memcpy memmove. Fixes #293

[kamphaus]

Fixes #293

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This change is 

[codecov]

Codecov Report

Merging #692 into master will decrease coverage by 0.03%.
The diff coverage is 95.34%.

@@            Coverage Diff             @@
##           master     #692      +/-   ##
==========================================
- Coverage   81.85%   81.82%   -0.04%     
==========================================
  Files         164      164              
  Lines        8875     8917      +42     
==========================================
+ Hits         7265     7296      +31     
- Misses       1208     1219      +11     
  Partials      402      402

Impacted Files	Coverage Δ
program/function_definition.go	100% <ø> (ø)	⬆️
transpiler/unary.go	74.55% <100%> (ø)	⬆️
darwin/string.go	100% <100%> (ø)	⬆️
noarch/string.go	100% <100%> (ø)	⬆️
util/goast.go	88.2% <81.81%> (-4.46%)	⬇️

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[elliotchance]

Reviewed 4 of 5 files at r1, 1 of 2 files at r2.
Review status: 5 of 6 files reviewed at latest revision, all discussions resolved, some commit checks failed.

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Comments from Reviewable

[elliotchance]

Reviewed 1 of 2 files at r2.
Review status: all files reviewed at latest revision, all discussions resolved, some commit checks failed.

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Comments from Reviewable