Returns a string with the Frame’s data formatted as a table, i.e. the same representation as displayed when trying to inspect the frame from Python console.
Different aspects of the stringification process can be controlled
dt.options.display options; but under the default settings
the returned string will be sufficiently small to fit into a
typical terminal window. If the frame has too many rows/columns,
then only a small sample near the start+end of the frame will be