Allow regular expressions in proxies definition

Wished behavior

I would like to be able to tell Karma to serve a file whatever the sub-path is. I could also want to transform the URL to something completely different. For instance, something like this (but it won't work with the object syntax):

proxies: {
    /\/images\/.*/: "/base/test/assets/placeholder.png",
    /\/books/(\d+)\/pages\/(\d+)/: "http://external.host/get_book_page.php?book_id=$1&page_id=$2"
}

Proposed syntax

proxies could accept an object, as it is currently the case, or an array of arrays, which is still readable, and accepts regular expressions as "keys":

proxies: [
    [/\/images\/.*/, "/base/test/assets/placeholder.png"],
    [/\/books/(\d+)\/pages\/(\d+)/, "http://external.host/get_book_page.php?book_id=$1&page_id=$2"]
]