feat: refactored the way the borders are added to the application

[kpagacz]

• removed firstcolumnborder and colspan_line arguments to gentlg
• added the matrix_border and the border_fns arguments to gentlg

[gmbecker]

@kpagacz can you please refresh this and clear the conflicts?

[kpagacz]

Updated:

• backwards compatibility when calling gentlg with defaults
• counting rows in the border matrix ignores the first title row
• tests
• more documentation and examples