404 handler js

Created by: zeffii

this removes the local 404.html and 404_custom.html and instead places only a single index.html in gh-pages of sverchok.github.io/missing_doc_handler

• https://sverchok.github.io/missing_doc_handler/index.html
  • code:https://github.com/Sverchok/missing_doc_handler/blob/gh-pages/index.html

this accepts url parameters, like ../index.html?param=somevalue . This allows us to customize the faux "404" landing page, by passing variables from python. Right now it expects only one parameter.

• on windows webbrowser.open(url) doesn't seem to like a local file being opened with url parameters attached.
• github gh-page seems like a convenient and non-interfering solution.
  • github seems to limit url parameters to only index.html ; f.ex. ..index2.html?p=param fails and returns a 404