refactor vim fn naming

vim/ftplugin/himalaya-msg-list.vim

@@ -8,7 +8,7 @@ nnoremap <buffer><silent>q     :bwipeout<cr>
 nnoremap <buffer><silent><cr>  :bwipeout<cr>
 nnoremap <buffer><silent><esc> :bwipeout<cr>
 
-call himalaya#shared#define_bindings([
+call himalaya#shared#bindings#define([
   \["n", "gm"  , "mbox#input"     ],
   \["n", "gp"  , "mbox#prev_page" ],
   \["n", "gn"  , "mbox#next_page" ],

vim/ftplugin/himalaya-msg-read.vim

@@ -1,7 +1,7 @@
 setlocal bufhidden=wipe
 setlocal buftype=nofile
 setlocal cursorline
-setlocal foldexpr=himalaya#shared#thread_fold(v:lnum)
+setlocal foldexpr=himalaya#shared#thread#fold(v:lnum)
 setlocal foldlevel=0
 setlocal foldlevelstart=0
 setlocal foldmethod=expr
@@ -9,7 +9,7 @@ setlocal nomodifiable
 setlocal nowrap
 setlocal startofline
 
-call himalaya#shared#define_bindings([
+call himalaya#shared#bindings#define([
   \["n", "gw", "msg#write"      ],
   \["n", "gr", "msg#reply"      ],
   \["n", "gR", "msg#reply_all"  ],

vim/ftplugin/himalaya-msg-write.vim

@@ -1,5 +1,5 @@
 setlocal cursorline
-setlocal foldexpr=himalaya#shared#thread_fold(v:lnum)
+setlocal foldexpr=himalaya#shared#thread#fold(v:lnum)
 setlocal foldlevel=0
 setlocal foldlevelstart=0
 setlocal foldmethod=expr