v0.4.0: Buffer messages until time information is valid

• Log messages get buffered until time information is available. This fixes #17. Filenames now include always the correct timestamp instead of point zero of unix time when logging in the first cpu cycles.
• TcLogCore exposes the TimeInfoReady property to indicate when the time information is available. This can be used have only valid timestamps within in the log files. It is a choice, though: either log from the first cycle on, risking to have an invalid timestamp for the message, or throwing away the first cycles and have only valid timestamps.