handle tbl-cap-location in cells

[cscheid]

We complete tbl-cap-location in cells, so we should support their use.

[cderv]

@cscheid does this cover only setting tbl-cap-location inside code cells ?

Or does it also cover the fact that tbl-cap-location does not work correctly with knitr tables even when set from main YAML header ? I am not sure what you have encountered and checking before opening a new issue.
I also see this know #1267 which was related but concerns in-cells only