mk_queue: Change mem.base type to char *.
deflate: Rewrite of deflate plugin.
mk_filter: Continue filters in order.

Don't call downstream filters unless there's data available.

Add mk_filter_abort(), mk_filter_body_is_done(), mk_filter_header_is_done().
Remove mk_filter_body_end() and mk_filter_header_end().
mk_http_transport: Avoid blocking output if possible.

Use HTTP chunked transfer if no length headers has occurred yet and the
transport allows it.
mk_http: Add length header if mk_response_body_fixed() is used.
mk_http: Update filter handling.
mk_request: Remove two filter request stages.
mk_plugin: Fix location prefix lookup.