Consistently using 'task' rather than both 'task' and 'command'
Renaming: 'source' -> 'tracked', 'target' -> 'original'
Renaming: '_each_dotfile' -> '_each_tracked_dotfile'

Better name given this function is the counterpart of
'_each_original_dotfile'
Moving options above environment.

In future versions, it's expected that some of the settings currently in
the environment section will be dependent on the options that have been
used.
Renaming: '_each_[tracked|original]_dotfile' -> '_each_[tracked|original]_file'

Using more generalized name for flexibility and, hopefully, clarity.