IAppender add MaxSeverity to filter log

[redfox1999]

Appender add MaxServerity to filter log

[SergiusTheBest]

Hi @redfox1999 ,

Thank you for the pull request! However IAppender doesn't need severity filter as logger already has one. So you basically need to create several loggers and link them together:

enum
{
    FileSink = 1,
    ConsoleSink = 2,
};

static plog::RollingFileAppender<plog::CsvFormatter> fileAppender("MultiAppender.csv", 8000, 3); // Create the 1st appender.
static plog::ColorConsoleAppender<plog::TxtFormatter> consoleAppender; // Create the 2nd appender.

plog::init<FileSink>(plog::debug, &fileAppender);
plog::init<ConsoleSink>(plog::warning, &consoleAppender);
plog::init(plog::debug, plog::get<FileSink>()).addAppender(plog::get<ConsoleSink>());

LOGD << "Hello!";

plog::get<FileSink>()->setMaxSeverity(plog::info);