Theming layer integration

This patch integrates the specific signs '^' and '{' when using Drupal's theme layer. So if you use 'table=theme' you're now able to merge cells. Moreover the patch eliminates the '!'-signs in this context, because always the first table row cells are considered as <th>. Finally it enables you to use phptemplate_table() or YOURTHEME_table() in the template.php of your theme to make final adjustments.

All this is somehow half the way, because I think the theme layer should be generally used for output. If this would be the case, then you would be extremly flexible: let's say you have this:

[table class=myclass summary=The_summary_of_this_table. caption=My_header
                   |  header A         | header B         | header C         |
                   |  contents cell 1  | contents cell 2  | contents cell 3  |
class=importantrow |  data 4           | data 5           |class=red  data 6 |
                   |  data 7           | ^ merged         | data 9           |
]

• A cell could begin and end with a '|' - and would give you 3 benefits: a) not to deal with Drupal's line break converter and b) to be able to add table row attributes at the beginning of a line and c) to have better usability since even the macro itself looks more like a table.
• I wouldn't specify attribute names - I would parse the first occurencies of foo=bar and treat them as attributes: on the table layer at the first row after '[table', on the row layer at each beginning of a line and on the cell layer after each '|'.

Does this make sense? What do ypou think?