Allow generating wiki and mediawiki tables

Allow generating wiki and mediawiki tables

* lisp/textmodes/table.el (table--generate-source-prologue)
(table--generate-source-epilogue)
(table--generate-source-scan-rows)
(table--generate-source-cells-in-a-row): Insert the wiki/mediawiki
separators.

* lisp/textmodes/table.el (table-source-languages): Add support
for wiki and mediawiki tables (bug#13287).

2019-06-27  Lars Ingebrigtsen  <larsi@gnus.org>

	* doc/emacs/text.texi (Table Misc): Mention the new wiki and
	mediawiki formats.