Error: issue #139; added more log output and module comments
wadindex|Roles/File: close #126; recompose checksumming

- Added new attributes `[md5|sha]_checksum_gen_time` to the `File`
  role
- Added a `Timer` object to the `gen_[md5|sha]_checksum` methods in
  `Roles/File`, populate the checksum generation time attributes in
  each of those methods when generating a checksum