vimwiki nested_syntaxes

Vimwiki does not support setting nested_syntaxes for temporary wikis, forcing use of Vim filetypes for syntax highlighting. Some Vim filetypes differ from [[https://highlightjs.org/|highlight.js]] and Pygments, disabling syntax highlighting, when converted to HTML.

vimwiki#vars#set_wikilocal('nested_syntaxes', vimwiki#vars#get_wikilocal('nested_syntaxes',1))