fix bug #41. nginx sample conf is error.
Merge pull request #42 from charlescui/master

fix bug #41. nginx sample conf is error.
add directive 'mruby_set' and 'mruby_set_inline'

These directives assign a result of mruby script to a variable.

mruby_set_inline $res1 "ARGV[0] + ', ' + ARGV[1]" "Hello" "World";
mruby_set        $res2 "/etc/nginx/script/hello.mrb";