Publish only required files

[MarkHerhold]

This PR removes unnecessary files (test, examples) when publishing to npm. Please see the npm docs on the files key in package.json.

To see how this will be packaged without publishing, run:

npm pack
# produces resolve-1.3.3.tgz

Files that will be published with this PR:

./index.js
./lib
./lib/async.js
./lib/caller.js
./lib/core.js
./lib/core.json
./lib/node-modules-paths.js
./lib/sync.js
./LICENSE
./package.json
./readme.markdown

Thanks for the awesome library!

[ljharb]

a) the "files" property is very dangerous; only .npmignore is a safe way to exclude files from publishing.
b) all files are required; npm explore foo && npm install && npm test should always work, for every package.

[MarkHerhold]

@ljharb Why do you say the "files" property is dangerous?

[ljharb]

If I add a new file that's needed in production, and forget to add it to "files", production breaks but all my tests pass.

If I add a new file that's not needed in production, and forget to add it to "npmignore", nothing breaks, and a package that's downloaded once and cached is insignificantly larger, until I notice the error.

The latter is maybe inconvenient; the former is likely breaking and thus user-hostile.