Added function to add new line.

[nxiss7]

I think adding new lines is a common task, it's a must-have feature for me.

[amiremohamadi]

Thank You for the PR!

I think it would be better to define new_line as a constant.
refer to python-docx library, we can define an enum/class (e.g BREAK) that has a value called LINE. So user can add a new line break like this:

p.add_run(duckx::BREAK::LINE);

Feel free to send PRs :)

[nxiss7]

Ok, will take look and update code.
:D

[nxiss7]

After a few busy weeks I could finally refactor the code.
I also added support for columns and tab character too.

[SimantoR]

This PR seems ready to be merged in. Any tests to add or verify for this?

[amiremohamadi]

This PR seems ready to be merged in. Any tests to add or verify for this?

Hi @SimantoR, it seems ready but after completing #81 this will be merged.