add console_formatter / console_logger to builder

[andrieshiemstra]

something like

console_formatter : Fn(&rt, &realm, ts: Instant, txt: &str, level: LogLevel) -> String
console_logger : Fn(&rt, &realm, msg: &str, level: LogLevel)

which may be used to override the default behaviour of the console feature

[andrieshiemstra]

overriding log gives enough flexibility,more tracking info will later be added with tracing