Addition/Modification of previewers to browser-side rendering

[slint]

Current previewers use Python libraries to do any kind of formatting/validation of the content on the server-side, thus wasting cycles for tasks that modern Javascript libraries perform perfectly fine (and sometimes even better than their Python alternatives) given the data on the client-side.

Extensions that could benefit from this kind of practice could be:

• csv: Already uses D3.js to render CSV data in table format.
• json: Using Json Formatter.
• md: Using Showdown.js.
• xml: Some browsers take advantage of XSLT to render XML nicely, given the appropriate HTML headers/tags. There are also a couple of Javascript XML renderers, but none of them is considered a de facto solution at the time.