Code syntax testing

- simple code tag (e.g. <php> echo "Hello World"; </php>) <php> echo "Hello World"; </php>

- advanced code tag

 echo "Hello World";

- advanced code tag with line numbers

 echo "Hello World";

- default code tag

 echo "Hello World";

- display a list of supported languages

- if invalid language argument, return the language list

 echo "Hello World";