Add an `mdbook rename` or `mdbook mv` command?

[fitzgen]

To rename a file and update all of the links to that file within the book.

Example

Initial State

Say I start out with the following book:

• src/SUMMARY.md:

  # Summary
  
  * [Foo](./foo.md)
  * [Bar](./bar.md)
  

• src/foo.md:

  Also check out [bar](./bar.md)
  

• src/bar.md:

  Wow!
  

Rename bar.md to wow.md

I want to rename bar.md to wow.md, but I don't want my links to break, so I run this command:

$ mdbook rename bar.md wow.md

Final State

And I end up with this final state:

• src/SUMMARY.md:

  # Summary
  
  * [Foo](./foo.md)
  * [Bar](./wow.md)
  

• src/foo.md:

  Also check out [bar](./wow.md)
  

• src/wow.md:

  Wow!