20240220 - v2.12.4

new g:asyncrun_rooter hook for root detection:

• each item in the g:asyncrun_rooter dictionary is a function pointer (or name).
• each function will be called to detect current buffer's root directory, until find one valid result.
• returns empty string to skip, see the example

let g:asyncrun_rooter = get(g:, 'asyncrun_rooter', {})
function! g:asyncrun_rooter.mydetect()
    if unable_to_detect
        return ''
    endif
    return '/path/to/root'
endfunc