feature request: allow specifying arbitrary paths with --keep

[bentyeh]

Consider the following file passed to --keep:

tag1,tag2	output_filename_base

Currently, --keep appears to adhere to the following rules:

1. Output filenames get a _# (default) or _R# appended (--keep-r1-r2).
2. The output_filename_base value cannot contain any whitespace. (As an example, see https://colab.research.google.com/drive/1XjXwg9OUp2YZ69LFzlS4DkmWp4ckg-Ub.)

I would greatly appreciate if these rules were loosened to allow arbitrary filenames that allowed whitespace and did not automatically append suffixes.

tag1,tag2	file0_filename,file1_filename,...

For example, tabs could be enforced to delimit the 2 columns, thereby allowing whitespace in the 2nd column.

[Yenaled]

New release should fix this