val create_output : map_output:(string -> string) -> Output.tcreate_output ~map_output creates a Log.Output.t which will print only Message.message to stdout, discarding any information about tags, levels, or timestamps.
map_output will be applied to each string before printing, and is expected to be used to replace portions of output or identify which log a message came from.
This function is best used with existing Log.ts, e.g. to replace Log.Global's outputs in expect tests. If you just want a full Log.t, see create below.