templater: return data in increasing chunk sizes Currently hgweb is not streaming its output -- it accumulates the entire response before sending it. This patch restores streaming behaviour. To avoid having to synchronously write many tiny fragments, this patch also adds buffering to the template generator. Local testing of a fetch of a 100,000 line file with wget produces a slight slowdown overall (up from 6.5 seconds to 7.2 seconds), but instead of waiting 6 seconds for headers to arrive, output begins immediately.