Proposal: New standard library functions

This PR demonstrates some helper functions that I am thinking about adding to Nextflow, to reduce some of the boilerplate code that I see in nf-core pipelines. For now I have added these functions to nf-boost so that they are easy to play with. If people like them, I'll try to add them to Nextflow. These functions are meant to minimize the use of custom classes like `Yaml` and `JsonOutput`, providing a simpler functional interface. Helper functions are documented in the [nf-boost README](https://github.com/bentsherman/nf-boost).