hashdeep-compare function: hash

Invokes hashdeep and generates a log file compatible with hashdeep-compare.

Syntax:
    hashdeep-compare hash path/to/target_dir path/to/output_log.txt

Notes:
    This function is optional, but recommended to ensure log compatibility.

    The above function call is equivalent to directly calling
        hashdeep -l -r -o f path/to/target_dir \
          > path/to/output_log.txt \
          2> path/to/output_log.txt.errors

    Note that if the output file or the error file already exists, the command
    will be aborted (hashdeep-compare will not overwrite existing files).

