[IMP] Allow dest version and help details
Improve to allow to indicate desired final version with -t parameter.
There are tree use case:
- want to update to last minor version in the same major version (indicating same major int -t parameter)
- want to analyze changes in requirements between two non correlative versions.
- want to homogenize major versions (if possible) in a "heterogeneous" requirements file (with multiple major versions)
Improve help on call (and readme)