Make sure we are I-JSON compatible

[reisub-de]

https://tools.ietf.org/html/rfc7493

This seems to be like a good idea for maximum interoperability

[hgn]

This is fine, there is noted that it MUST be encoded in utf-8. But ASCII is compatible to utf8, so we are still using utf8 at sending process. The receiving process must be utf8 capable anyway. Thank you!

This RFC should be referenced in the ID!