Add a config

[CosmicHorrorDev]

Resolves #16

Nothing really too crazy to mention. I opted for having separate a separate Cli and Config struct that gets consolidated into the final Opts used throughout the program, so that things work fine if distinct values are added to Config that aren't present in Cli

This pulls in basic-toml which is a library by dtolnay that aims to be a simpler alternative to the current toml crate

[CosmicHorrorDev]

Yeah, I thought the same thing 😅

I think it would be worthwhile to add negated boolean flags. Adding it to my to-do list!

[Aloso]

@CosmicHorrorDev Sorry, I totally forgot about this. I'll release a new version next week as soon as I find the time.