Feature Request: Left Header

[DeStRoYeR-droid]

Description

Left side column needed (kind of like a left header). Useful when displaying information as is the case when displaying a matrix containing operation pertaining to the combination of left and top headers.

[DeStRoYeR-droid]

Adding more detail on what I meant, since the original description was light.
I know showindex=<iterable> already lets you prepend a left-most column of values, so as a plain-text grid this is close to achievable already:

tabulate(matrix, headers=['x','y','z'], showindex=['a','b','c'], tablefmt='grid')

But showindex prepends the index onto the row data before formatting, so the resultant left column ends up rendered as a data cell, not a header cell.

I'd like to take a crack at implementing this myself -- probably as a rowheaders parameter. Plan would be plain-text formats first (reusing the existing index-prepending logic).