Investigate related iframe libraries

[gordonwoodhull]

Creating this issue mostly to save the link:

ramnathv/htmlwidgets#252

A lot of the custom code in rcloud.htmlwidgets has to do with sizing the iframe properly. I don't know if this is the same issue that widgetframe and pym.js address, but it's worth taking a look.

At the very least there may be some techniques we can learn from those libraries.