Downstream webpack will need any dependencies src/ depends on so it can
successfully build. Also if multiple packages being built into a larger
script share a common dependency version range, they can share the
dependency instead of duplicating it. This will save built file size,
execution time, and memory.
Add `.gitattributes` for consistent line endings across platforms.
Use `node` instead of deprecated `stable` version specifier for Travis.
Set dev tool to `cheap-module-source-map`.
