support multiple prompt {file:...} directives

[nrbrd]

this is a small tweak in the config loader to support handling multiple file references in the config, so we can have something like this:

{
    "mode": {
        "foobar": {
            "prompt": "{file:./prompts/foo.txt}{file:./prompts/bar.txt}"
        }
    }

for example

[josephschmitt]

Doesn't the prompt key support an array of strings?

[nrbrd]

not, it only supports a string