Simple-file-poller

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- `keyboard_interrupt` method is now public

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- fixed race condition between watchdog reacting to new files and watchdog checking for files at specific intervals
- logging now distinguishes between DEBUG/INFO/ERROR levels
- keyboard interrupts via CTRL+C are now handled correctly
- in watchdog mode, an initial scan of the input directory is now performed, in case files were already present

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- added `params` object to allow attaching of arbitrary parameters to be used by the `check_file`
and `process_file` methods; this avoids accidentally overriding Poller attributes that were
introduced in later versions.

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- added support for using watchdog for reacting to file creation events, speeding up polling

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- `poll` method now skips directories, which could be listed if no extensions are supplied to restrict the polling.

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- added `other_input_files` glob list and `delete_other_input_files` to manage additional files that may
reside in the input directory along side the actual files that are being processed.