Update API Docs

[GretaCB]

• Add documentation.js compatible comments to the new standalone functions
• npm run docs: Remove installing documentation.js every time
• Add docs around installing documentation.js and how to create docs for new code

cc @mapbox/core-tech

[codecov-io]

Codecov Report

Merging #47 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #47   +/-   ##
=======================================
  Coverage   97.61%   97.61%           
=======================================
  Files           5        5           
  Lines         126      126           
=======================================
  Hits          123      123           
  Misses          3        3

Impacted Files	Coverage Δ
src/standalone/hello.cpp	100% <ø> (ø)	:arrow_up:
src/hello_world.cpp	100% <ø> (ø)	:arrow_up:
src/standalone_async/hello_async.cpp	94.59% <ø> (ø)	:arrow_up:

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