scribble/base: add `#:{column,row,cell}-properties` arguments to `tabular`

The new arguments greatly simplify adding properties such as alignment
and (HTML) background colors to table cells. For example, to make a
table with 'right alignment for the left-hand column, 'center alignment
for the second column, and 'left alignment for all remaining columns:

 (tabular cells
          #:sep (hspace 1)
          #:column-properties '(right center left))

Also, make `color-property` and `background-color-property` recognized
as table-cell style properties.

Finally, implement horizontal alignment for text rendering.