Add support for shell session highlighting in Confluence

The code macro in confluence allows to highlight many languages and is quite useful, but often I've found that I need to describe bash shell sessions in confluence.

The closest highlighter that Confluence has for this is bash, but it interprets all of the lines as shell script and can not be used to show output from a shell session in the code block.

Ideally, the shell session highlighter would only treat lines starting with #, $, > or user@linuxbox (or anything that looks like a command prompt) as code and all the rest as comments or output.

There's pretty good overview of different highlighting options and their expected effects in this Pygments shell-session lexer demo (or just see the[ comparison of different "modes" of highlighting|http://jann.cc/pygments-shell-session-lexer-demo/shell_code_comparison.html]).