initial import from github.com/cihub/seelog

imported commit:
https://github.com/cihub/seelog/blob/5e83c34ad339ec49e50628f8b0fd86bfbfd78f68/writers_rollingfilewriter.go
https://github.com/cihub/seelog/blob/5e83c34ad339ec49e50628f8b0fd86bfbfd78f68/writers_rollingfilewriter_test.go