Allow serializing JSON directly to a stream.

[tmccombs]

No description provided.

[rudolph-miller]

How about with :octets t ?

[tmccombs]

Right, I forgot to mention that it only works with character streams, and octets t overrides it.

Actually, I just thought of a way to add support for octet streams without too much effort, I'll add that to this pull request.

[rudolph-miller]

I won't merge any PRs without tests. :(
Please add test cases includes :stream stream and :stream stream :octets t.

And, it's better to me to rename keyword :stream to :output because stream can be input or output. :)

[rudolph-miller]

And, I saw PR in fast-io.
After this PR is merged, I will remove (fast-io::flush *stream*) .

[tmccombs]

Hmmm, I need to update compile-encoder and the compiler macro as well.

[tmccombs]

I played around with it for a while, but eventually realized that the evals execute the code in a null lexical environment, which makes it difficult to capture the output stream. If you have any ideas on how to get compile-encoder to work with an output stream I would be happy to help implement it.