Code splitting and building

[edemaine]

Currently, the compiled svgtiler.js file (158kB, 42kB gzipped) has a lot of code that is command-line-specific, and doesn't make sense for a web-only build. Also, we don't include any dependencies in a web build.

• Separate source files into base svgtiler.coffee and nodetiler.coffee which requires svgtiler.coffee.
  • Ideally all simulated-on-web imports like path would only be needed in latter, so we could remove these simulations.
  • For Node, package.json's bin and main point to nodetiler.js
• Plausibly split into separate files for each class, for easier code navigation.
• Web-specific builds in dist built by rollup or Parcel or webpack
  • Full build including CoffeeScript, @babel/standalone for JSX, Stylus, csv/xls parsers, etc.
  • Intermediate builds with different subsets?
  • May need a bare build seperate from svgtiler.js (in case of further splitting, and to fully avoid require/import).
• Alternatively, can we use code splitting features to automatically load dependencies as needed? This is challenging given how the code is currently written synchronously.
• Alternatively, can we just rely on dependencies being globally attached to window? Ideally each class could specify its dependencies, and expect the user to (lazy) load them before instantiating that class.
• Provide tree-shakable ESM source (I guess in lib). nodetiler.js won't be tree-shakable because of svgtiler megafunction (or can Parcel figure it out?), but that's Node anyway; svgtiler.js (for web) should be possible.
• svgink could similarly split off its CLI code so it doesn't up in any build of svgtiler (as we never need it).