Feature request: Preserve quotes in YAML frontmatter

[asmaier]

At the moment frontmatter will change the quotes around string values in a YAML frontmatter to single quotes even if the string value itself did not change at all. It would be nice if frontmatter would offer a option preserve_quotes like ruamel.yaml

https://stackoverflow.com/questions/42094599/preserving-quotes-in-ruamel-yaml

Such an option would prevent unnecessary changes to a file updated with frontmatter and would make the git history of such files more clean.