Improve bash lexer to support math:
Improve bash lexer to support math:

{{{
echo $(( 1 + 2 ))
}}}

zmughal/pygments-mirror,zmughal/pygments-mirror,sol/pygments,sol/pygments,zmughal/pygments-mirror,sol/pygments,zmughal/pygments-mirror,zmughal/pygments-mirror,zmughal/pygments-mirror,sol/pygments,sol/pygments,zmughal/pygments-mirror,zmughal/pygments-mirror,zmughal/pygments-mirror,zmughal/pygments-mirror,sol/pygments,sol/pygments,zmughal/pygments-mirror,zmughal/pygments-mirror,zmughal/pygments-mirror,zmughal/pygments-mirror,sol/pygments,zmughal/pygments-mirror,zmughal/pygments-mirror,zmughal/pygments-mirror,sol/pygments,sol/pygments,sol/pygments,sol/pygments,sol/pygments,sol/pygments,zmughal/pygments-mirror,zmughal/pygments-mirror