Refactor loaders to return a list of tags/tasks rather than modifying a passed in list without returning anything.
Ignore log and pid files for sumd
Fairly large refactor of sumd's main binary.

Changes include:
  - Options for log, config, and running directories
  - Refactor into main() and load_config() methods
  - Add pidfile handling methods
  - Add support for 'start' and 'stop' commandline args
  - Support stopping other sumd procs with 'bin/sumd stop'