Make invocation loc.body() default to all columns and rows

[rich-iannone]

When adding styles through the tab_style() method, it is far more sensible target the most number of cells and use the columns and rows arguments to constrain the cell selection. This PR enables this behavior so that this

import great_tables as gt
from great_tables import style, loc, md, html
from great_tables import exibble

(
    gt.GT(exibble)
    .tab_style(
        style=style.text(color="red"),
        locations=loc.body(),
    )
)

results in

Fixes: #76