%to-json fails on strings which aren't simple

[fisxoj]

I was working on something using mito and my strings from postgres were coming back as (vector character)s. Despite there being a ((string string)) method for %to-json, it actually requires strings to be simple-string in %write-string.

I have a solution that creates two methods, one for simple-string that does what the current string method does, and another on string that prints the string into a new simple-string. I'll post that, shortly.

[rudolph-miller]

Thank you to report. I'll review your pull-request then. :octocat: