refactor
fix race/panic on modify+delete

This fixes a race condition when a file is modified and unlinked in the OS before the inotify IsModify event has a chance to call os.Stat.
Fixed stop hang & stop err
Merge pull request #17 from presbrey/patch-1

fix race/panic on modify+delete
combine two if conditions
Merge pull request #18 from miraclesu/fix_stop_hang

Fix a hang in `Stop` when tailing a non-existent file

Reproducible on linux, but not on mac.