Add support for values that contain newlines + add tests that cover the full table output

[ddworken]

Thank you for this library! I used it in one of my projects and it is super helpful.

I recently realized that the behavior if someone does tbl.AddRow("foo\nbar") is slightly non-optimal. Currently, it has no special handling for this and thus the table formatting gets messed up.

With this PR, it will instead display it correctly spread across multiple rows. For example, here's a table rendered with "foo" and "bar" as the headers and with the single call tbl.AddRow("1\n2", "x\ny\nz"):

foo      bar
1        x
2        y
         z

WDYT of this change?

[ddworken]

@rodaine What do you think of this change?

[rodaine]

Sorry for the delay! Love it. 👍🏽