Command to remove every second selection

[Ordoviz]

I suggest adding commands to remove the odd-numbered or even-numbered selections. These would be helpful when you want to

• select every second line
• convert straight quotes into smart quotes (e.g. "foobar" into “foobar”) in two passes: First replace every opening double quote with a “ characters then closing double quotes with ”
• convert text with inline LaTeX formulas like $x^2$ into HTML, e.g. replace every odd dollar sign with an opening <math> and every even dollar sign with a closing </math> element