Use sindresorhus/node-defaults instead of deep-merge

[benasher44]

sindresorhus/node-defaults already has checks to prevent prototype pollution. Switching to that may be easier than patching deep-merge

[75lb]

I factored deep-merge out of the project, replacing it with hand-rolled code. Released in table-layout v4.1.1. Let me know if there's anything else, thanks.