Please explain your intent
The Table feature is fantastic, but I find that I want more control over borders that is provided by TableBorderLayout. I would really like to be able to control exactly which borders are turned on, and ideally also their thickness, independently.

Describe the solution you'd like
I was thinking that perhaps:

1. TableBorderLayout could become a regular class instead of an enum, so that a user could create instances of it
2. The existing values (e.g. HORIZONTAL_LINES) could still be class variables so that existing usage doesn't break
3. The class would hold on to a function/lamba that is called for every border segment for a table, and would return perhaps a thickness (0=off?) and a color (so table borders don't have to be black).

For (3) I'm imagining the function looking something like:

def should_render(rownum: int, colnum: int, is_header: bool, is_footer:bool, side: ?) -> ...?

Additional context
I'm actually trying to port some nasty Rmarkdown -> latex -> PDF code, and users have gotten used to some latex table styling, which I can't reproduce. One example is a table with i) thick borders above/below the table, ii) thin borders under the headerline, iii) no other borders.