LaTeX writer - support new table features

[jgm]

Adjust LaTeX writer to support new table features introduced in
jgm/pandoc-types#66
including table attributes (including identifier), rowspan, colspan, table head and foot, multiple header lines, row headers, captions that allow block-level content and include an optional short caption.

[stroobandt]

The CALS table model

Perhaps of interest to this discussion is the the CALS table model.
CALS started out as a United States Department of Defense (DoD) initiative for creating a DTD standard for representing tables in SGML/XML.

CALS allows for cell merging.

CALS is also the historic precursor of the HTML table model. A little known fact is that CALS is supported in LaTeX through the cals package. In fact, it is easier to use and offers more capabilities than the more commonly employed tabularx package in LaTeX.

Here is the documentation of the cals package in LaTeX:

• http://www.ctan.org/tex-archive/macros/latex/contrib/cals (demo & doc)
• http://tug.org/TUGboat/tb32-2/tb101parashchenko.pdf (user's manual)

[the-solipsist]

Just FYI: There's an existing open issue on the CALS table model: #890 (opened by @stroobandt himself in 2013).

[stroobandt]

@the-solipsist Thanks for pulling CALS out of the woodwork again!

It surely is a nice standard to work from and it is already supported in at least LaTeX and, by definition, in HTML.
Furthermore, it allows to merge cells. This is currently not supported in Pandoc Markdown.

If the CALS standard is good enough for the US military, it is probably also good enough for the rest of us.

[tarleb]

Possibly incomplete list of missing features:

• Row headers
• Intermediate header rows (body headers)
• footers

Should we open separate issues for each of these? Implementing table footers might be an excellent first issue.