move foldtext to autoload function

autoload/myfold.vim

@@ -0,0 +1,25 @@
+function! myfold#text()
+    " get actual numberwidth of the current document
+    let nw_add = (len(line('$')) - (&numberwidth - 1))
+    if nw_add > 0
+        let nw = &numberwidth + nw_add
+    else
+        let nw = &numberwidth
+    endif
+
+    let numfold_w =(nw * &number) + &foldcolumn
+    let window_w = winwidth(0) - numfold_w
+    let onetab = strpart('          ', 0, &tabstop)
+
+    let foldtxt_start = getline(v:foldstart) . '  …'
+    let foldtxt_start = substitute(foldtxt_start, '\t', onetab, 'g')
+    let foldtxt_start_w = len(foldtxt_start) - 2
+
+    let foldtxt_end = '+' . string(foldclosedend(v:foldend) - foldclosed(v:foldstart)) . '         '
+    let foldtxt_end_w = len(foldtxt_end)
+
+    let foldtxt_mid_w = window_w - (foldtxt_start_w + foldtxt_end_w)
+    let foldtxt_mid = repeat(' ', foldtxt_mid_w + 2)
+
+    return foldtxt_start . foldtxt_mid . foldtxt_end
+endfunction