Tikz support

Instiki now (optionally) supports

\begin{tikzpicture}
...
\end{tikzpicture}

and

\begin{tikzcd}
...
\end{tikzcd}

environments. To enable, start a tikz server (either local or remote)
and uncomment the last line of config/environments/production.rb

Gemfile

config/environments/development.rb

config/environments/production.rb

config/environments/test.rb

lib/chunks/tikz.rb

lib/sanitizer.rb

lib/wiki_content.rb

test/unit/chunks/tikz_test.rb