Impossible to emit booleans using encode-json

[libre-man]

A the moment it is impossible to emit booleans using the encode-json functions. It possible to do this using jonathan directly, by supplying the :false keyword. This does not working using datafly because the keyword gets removed in the typecase in convert-for-json.

This could be solved modifying this typecase, however it might be better to remove the typecase and use CLOS instead. This way the code is more extendable and the user could change the behavior them self.