Add fileeater program

Adds the fileeater program that monitors the contents of a file. It is a simplification of tail -f logfile.txt | moneater.py mypkg.BestEater that is used for most monitoring. Now one can do fileeater logfile.txt mypkg.BestEater.

The fileeater program also supports multiple files with individual eaters from a fileeater specification YAML file. For example:

monitor:
  - eater: pbv3.eater.StatusEater
    file: '{logdir}/pb.err'
    table: Status
  - eater: pbv3.eater.CorrSEUEater
    file: '{logdir}/pb.err'
    table: CorrSEU
  - eater: pbv3.eater.SEUEater
    file: '{logdir}/pb.err'
    table: SEU

The following improvements are also included:

• Added a monexec package that contains helper functions for common tasks of moneater programs (moneater, fileeater).
• InfluxDB configuration can be stored in a YAML file. See README for format.