ad­dlines – A user-friendly wrap­per around \en­largeth­is­page

This small pack­age pro­vides the com­mand \ad­dlines for adding or re­mov­ing space in the textblock of the page it's used on. E.g., adding an ex­tra line of text to the page so that a sec­tion fits bet­ter on the next page.
It will also add space to the fac­ing page in a two-sided doc­u­ment.