can you add a support for custom cap name in options

[jipengzhu]

i have a symbol link file which name is different from the target file,
in order to insert the code, i have to use the url of target file rather than symbol link file
so i want to custom the cap name because the target file name is not i want

i make a pr for this, if you accept it, please update the README

thx

@nkmk