Dasel V3

Dasel V3 contains a pretty substantial rewrite.

The entire select syntax/language is being rewritten. We will have a proper lexer + parser with what I hope to be a much more intuitive syntax.

This fixes whitespace issues, supports standard arithmetic operations without using functions, and opens the door to exciting new features such as an interactive terminal cli.

This is still very much a WIP, and will definitely contain breaking changes.

You can view the rough syntax in the tests here: https://github.com/TomWright/dasel/blob/v3/execution/execute_test.go

I'm open to feedback and suggestions.