Add option to not escape / in output of JSON filter

[Former user]

Original issue 410 created by @ysavourel on 2014-07-25T11:00:32.000Z:

The character / can be escaped or not according the JSON specification.
Many users would like to not escape it.
We should have an option to select either way.

[Chase Tingley]

I was looking at this briefly. This would really be a fix to the JSONEncoder, and we're playing with fire a little bit with the way that the filter parameters are passed to JSONEncoder, because JSONEncoder parameters (currently just "escapeExtendedChars") aren't namespaced in any way. It would probably be better to use a prefix like "jsonEncoder.escapeExtendedChars" to avoid colliding with a hypothetical filter option with the same name.

[Chase Tingley]

Fixed by David Miekle.