Allow custom indices per list

Implements #338

autoload/startify.vim

@@ -91,7 +91,7 @@ function! startify#insane_in_the_membrane() abort
   endif
   call append('$', g:startify_header)
 
-  let b:startify = { 'tick': 0, 'entries': {} }
+  let b:startify = { 'tick': 0, 'entries': {}, 'indices': [] }
 
   if s:show_special
     call append('$', [s:padding_left .'[e]  <empty buffer>', ''])
@@ -454,6 +454,8 @@ function! s:show_lists(lists) abort
       continue
     endif
 
+    let b:startify.indices = copy(get(list, 'indices', []))
+
     if type(list.type) == type('')
       if has_key(list, 'header')
         let s:last_message = list.header
@@ -924,7 +926,9 @@ endfunction
 
 " Function: s:get_index_as_string {{{1
 function! s:get_index_as_string(idx) abort
-  if exists('g:startify_custom_indices')
+  if !empty(b:startify.indices)
+    return remove(b:startify.indices, 0)
+  elseif exists('g:startify_custom_indices')
     let listlen = len(g:startify_custom_indices)
     return (a:idx < listlen) ? g:startify_custom_indices[a:idx] : string(a:idx - listlen)
   else

doc/startify.txt

@@ -151,13 +151,18 @@ This option is DEPRECATED in favor of |g:startify_lists|.
           \ { 'type': 'commands',  'header': ['   Commands']       },
           \ ]
 <
-Startify displays lists. Each list consists of a type and an optional header.
+Startify displays lists. Each list consists of a `type` and optionally a `header`
+and custom `indices`.
 
 The 'type' is either a string of a built-in type or a |Funcref|.
 
 The 'header' is a list of strings, whereas each string will be put on its own
 line in the header.
 
+The 'indices' is a list of strings, which act as indices for the current list.
+Opposed to the global |g:startify_custom_indices|, this is limited to the
+current list.
+
 Built-in types:~
 
 'files'