number support

[macintux]

Would be useful to support numeric values as alternatives to textual values.

Currently:

-type text() :: {text, iolist()}.
-type column() :: {column, iolist(), [iolist()]}.
-type table() :: {table, [{iolist(), iolist()}]}.

Proposed:

-type text() :: {text, iolist()}.
-type column() :: {column, iolist(), [iolist()|number()]}.
-type table() :: {table, [{iolist(), iolist()|number()}]}.

Optionally: -type numeric() :: {numeric, number()}.