Added useCompactFormat flag to support posting events using Serilog.Formatting.Compact

[nblumhardt]

The compact format in Serilog.Formatting.Compact is faster to emit and more compact on the wire.

Usage:

Log.Logger = new LoggerConfiguration()
    .WriteTo.Seq("http://localhost:5341", useCompactFormat: true)
    .CreateLogger();

This will cause the sink to send newline-delimited compact events to /api/events/raw with the content type application/vnd.serilog.clef. This requires Seq 3.3, which should be available on the downloads page in about 8 minutes ;-).