This SRFI is so useful that I already started using the sample
implementation even though it's work in progress :) I'd like to use it
from more Scheme implementations than just Chibi.

Do you accept the following changes?

- Rename the library from (json) to (srfi 180)

- Rewrite `maybe-read-number` so it doesn't rely on regular expressions
and `string->number`. This would remove the dependency on (chibi regexp)
making it easier to port SRFI 180 to other R7RS Schemes.

I can send a PR, or if you prefer to do them yourself, I'll wait. I
already sent a PR with some trivial changes today; hope they're OK.