Add Option to log only last x 1000 lines in debug.log

In config.toml there is the option

output_limit 	Set maximum build log size in kilobytes, by default set to 4096 (4MB)

If a log gets bigger than this limit it is truncated at the end which in most cases lets you miss the important errors on a build-failure which are probably near the end of the build process.

It would be most helpful if the log would be truncated at the beginning of the log file instead.

maybe we can add an option that defines how many lines from the end you want to keep in case the output_limit is exceeded.