Fixes #221.

For wiki syntax tables, add `wiki_style_separator` as an attribute
for the Tag node. Also reorder `closing_wiki_markup` property and tests
to match its place in the constructor.

Tables and rows use newlines as padding, partly because these characters
are pretty important to the integrity of the table. They might need
to be in the preceding whitespace of inner tags instead as padding after,
not sure.

Added support for allowing different wiki syntax for replacing the opening
and closing tags. Added for table support.

Still need to do attributes.

* Some other fixes, additions.