Add syntax files from upstream vim repository

ftplugin/btm.vim

@@ -0,0 +1,16 @@
+if !exists('g:polyglot_disabled') || index(g:polyglot_disabled, 'vim') == -1
+  
+" Vim filetype plugin file
+" Language:	BTM
+" Maintainer:	Bram Moolenaar <Bram@vim.org>
+" Last Change:	2004 Jul 06
+
+" Only do this when not done yet for this buffer
+if exists("b:did_ftplugin")
+  finish
+endif
+
+" Behaves just like dosbatch
+runtime! ftplugin/dosbatch.vim ftplugin/dosbatch_*.vim ftplugin/dosbatch/*.vim
+
+endif