Code folding with RMarkdown

[ghowoo]

I am using Emacs-polymode-Ess-R writing RMarkdown code to deliver analysis and report. It has been amazing except for several small nuisances. Thank you for the excellent work.

One is about the folding of codes. It is nice to use the tab key to fold by levels, # of the first level, ## of the second level, etc. However, it does not fold the yaml part, the contents contained in ---. Or in other words, it would be nice to have a function to fold the code section, between the two ```.

Another is if there could be a function to select all codes in the chunk or within the boundary of ```. I often narrow down to the current chunk to write or modify codes.

Thanks.