Loosen unprintable character sanitization to not remove valid line-endings

So @inpermutation and I noticed that some feeds with `\r` or `\n` had words running together.

Example:

`This is a test\r\ncase`

Was displayed as 

`This is a testcase`

We were too aggressive with our fixing of #295 - `[:print:]` is catching `\r\n` so let's explicitly fix the weird JSON unicode chars (this aligns with the rack fix as well: https://github.com/rack/rack-contrib/pull/37/files).