Convert FrontMatterDocument back to raw String

[mpfaff]

Could there be a method to convert a FrontMatterDocument with modified data and content back to a raw String? I'd probably be willing to help if it's something you'd consider.

[mpfaff]

@izolate Bumping this issue

[izolate]

Hi @MaterialTime, considering anything people find useful! What do you have in mind for this method? Can you give an example?