Convert to ES module

[stilist]

This PR converts the code to use ES6+ features:

• import dependencies
• convert plugin from extending L.Control to a native ES class
• export plugin (though it's also still declared as L.Control.GlobeMiniMap, so it's API-compatible)

I was careful to only make syntax changes, and leave the code inside the functions alone.

To support these changes, I added a Webpack setup that automatically generates a UMD wrapper for the imports and compiles the class down to ES5. This does result in a ~50% increase in the size of the compiled and uglified JS (from 3375 bytes to 5264 bytes), but once this PR lands the plugin can be refactored to get the build size back down.

Other changes:

• Add change log file
• Add EditorConfig
• Reformat source for consistent two-space indentation — this makes the diff look really big, but you can view it with whitespace changes hidden to see what's actually different

[stilist]

Also, I updated the package version from 0.0.1 to 0.1.0 in package.json, because 1) I think this plugin is pretty reliable, and 2) it's technically accurate SemVer because the topojsonSrc option was added after 0.0.1. (New features require incrementing the minor version number.)

I think it would be good to publish a Github release some time soon, though perhaps after the refactor I referenced in the PR?