Build in alternative table styles

[tdwright]

Rather than hypens, pipes and pluses, we should be able to switch to other "themes" for tables.

The default might looks like this:

+-------+--------+
| Apple | Orange |
+-------+--------+
| 12    | ABC    |
| 123   | AB     |
+-------+--------+

And we may want (for instance) to be able to use hashes and equals signs:

#=======#========#
# Apple # Orange #
#=======#========#
# 12    # ABC    #
# 123   # AB     #
#=======#========#