CLI refactor commands

[NQNStudios]

It struck me that one thing that's currently difficult is renaming sections in Markdown, especially the more they're referenced in links and macros. Here's a functionality idea that will also benefit us when it comes to making an editor:

fractive refactor @Section @NewSectionName -- searches all Markdown files and updates the section declaration as well as any macro references to @section

Gotcha: sections can also be referenced in code and those cases will be harder (or impossible) to detect programmatically and fix.