Simplify Package

Added

• Better TypeScript support for array flattening

Changed

• Added ES2015 distributable and renamed primary export to exports.flatten

Removed

• Removed array type checked entry to flatten, prefer performance and smaller code
• Removed depth version of functions, if you know the depth it's better to use something like Array#flat or flatten helpers explicitly in code - you typically don't need anything between 1 and infinity in every day code