Feat: Add flag aliases feature

[oNaiPs]

@SupImDos first of all, thanks for such a useful project!

This PR attempts to implement #44.
It seems to have the functionality, however I'd like your guidance regarding next steps:

• What do you think of the implementation approach?
• Docs
• More Tests

Some comments regarding these edge cases:

What happens if you provide alias and aliases?
What is the behaviour for boolean arguments
What is the behaviour for inverted arguments (i.e., --no-<x>)

It seems to me that alias and aliases target different cases. Since alias maps to argparse's dest field, the optional aliases flags you set up would not alter this behavior.
In regards to the boolean option, BooleanOptionalAction should take care of it (if option starts with --, negates)
Finally, regarding inverted arguments, not sure what would be the case here, could you give an example?

Closes #44.