Add a proper upper limit (4096 seems enough for now) and safely NUL-terminate the rbuf. The idea is to later drop the clt->buf static buffer and allocate it on demand only when we need to do (http) chunking.

This allows amused-web to stay in sync using websockets (much like existing amused clients watch `amused monitor') and sends the forms in the background to avoid refreshing the page. Still missing is reopening the websocket, maybe blocking the UI in that case and showing the progress.

w3m (HTTP/1.0) doesn't seem to like it.

It's a first stab at it, some planned features (like the search) are missing but the basic ones work. It's not hooked in the main build yet.