Support of captions on subfigures

[miguelfm]

No description provided.

[pfitzseb]

Could you add a test for this?

[miguelfm]

Could you add a test for this?

I have tested with this in my system.
test.jmd

---
crossref:
options:
    doctype: pandoc2pdf
    fig_ext : .pdf
---
<div class="subfigures" id="fig:AB"> 
![figA](A.pdf){#fig:A width=50%} 
![figB](B.pdf){#fig:B width=50%} 

Caption both figures
</div>

Without the lines to add the sub/caption packages in "pandoc_header.txt" this error is generated:

Error producing PDF.
! Undefined control sequence. 
l.57 \subfloat