Output function for using markmap within Shiny applications and interactive Rmd documents. This function is taken from https://github.com/seifer08ms/Rmarkmap.
markmapOutput(outputId, width = "100%", height = "400px")output variable to read from
Must be a valid CSS unit (like '100%', '400px', 'auto') or a number, which will be coerced to a string and have 'px' appended.
See 'width'.