wordcount: move User autocommand to plugin

Do not scatter the autocommands around, but rather move the auto command
to the main plugin file. The function that handles the auto command will
be created in the autoload script.

Also add a call to force updating the tabline, if g:airline_statusline_ontop
is defined.

In addition, the wordcount() extension did not correctly notice
block-wise visual mode, so while creating the airline#mode_changed()
function, make the mode also detect blockwise visual mode correctly.

autoload/airline.vim

@@ -271,3 +271,11 @@ function! airline#update_tabline()
     call airline#extensions#tabline#redraw()
   endif
 endfunction
+
+function! airline#mode_changed()
+  " airline#visual_active
+  " Boolean: for when to get visual wordcount
+  " needed for the wordcount extension
+  let g:airline#visual_active = (mode() =~? '[vs]')
+  call airline#update_tabline()
+endfunction

autoload/airline/extensions/wordcount.vim

@@ -68,9 +68,8 @@ function! s:update_wordcount(force_update)
   endif
 endfunction
 
-let s:visual_active = 0  " Boolean: for when to get visual wordcount
 function airline#extensions#wordcount#get()
-  if s:visual_active
+  if get(g:, 'airline#visual_active', 0)
     return s:format_wordcount(s:get_wordcount(1))
   else
     if get(b:, 'airline_changedtick', 0) != b:changedtick
@@ -109,9 +108,5 @@ function! airline#extensions#wordcount#apply(...)
 endfunction
 
 function! airline#extensions#wordcount#init(ext)
-  augroup airline_wordcount
-    autocmd! User AirlineModeChanged nested
-          \ let s:visual_active = (mode() ==? 'v' || mode() ==? 's')
-  augroup END
   call a:ext.add_statusline_func('airline#extensions#wordcount#apply')
 endfunction

plugin/airline.vim

@@ -145,6 +145,7 @@ function! s:airline_toggle()
       autocmd BufWritePost */autoload/airline/themes/*.vim
             \ exec 'source '.split(globpath(&rtp, 'autoload/airline/themes/'.g:airline_theme.'.vim', 1), "\n")[0]
             \ | call airline#load_theme()
+      autocmd User AirlineModeChanged nested call airline#mode_changed()
 
       if get(g:, 'airline_statusline_ontop', 0)
         " Force update of tabline more often