Do not reuse the last logfile if it was already archived
Merge pull request #295 from georgekola/master

Do not reuse the last logfile if it was already archived
Store NSDateFormatters in thread-attached storage to avoid wasteful + expensive recreation of these objects.
Adjust key used for formatter thread-attached storage
Once more - adjust naming convention for thread-safe dictionary keys
Merge pull request #296 from talko/formatter

Store NSDateFormatters in thread-attached storage to avoid wasteful + ex...
Returning new instance correctly.
Merge pull request #301 from arturogutierrez/formatter_fix

Returning new instance correctly