Fix printing bugs when using no-overwrite flag

[aemous]

Description of changes:

• Fixed bug when using --no-overwrite parameter where the last character printed to CLI would be a carriage return (\r), which would cause incompatibility with some terminal program (e.g. Windows Powershell).
  • Keep track of files skipped for determining whether there is progress remaining in ResultPrinter.
  • Update files remaining progress to take into account files skipped.
  • Add support for results that do not print newlines (e.g. new SkipFileResult).
  • Modify result handling in ResultPrinter so that they can opt-out of resetting progress_length to 0. Useful for result handlers that do not print newlines (e.g. new SkipFileResult).

Description of tests:

• Manually tested changes on Windows Powershell, with uploads, bucket-to-bucket copies, and downloads. Verified the bug is fixed in all three cases.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.