Add syntax files from upstream vim repository

syntax/rng.vim

@@ -0,0 +1,29 @@
+if !exists('g:polyglot_disabled') || index(g:polyglot_disabled, 'vim') == -1
+  
+" Vim syntax file
+" Language:    RELAX NG
+" Maintainer:  Jaromir Hradilek <jhradilek@gmail.com>
+" URL:         https://github.com/jhradilek/vim-rng
+" Last Change: 25 March 2013
+" Description: A syntax file for RELAX NG, a schema language for XML
+
+if exists('b:current_syntax')
+  finish
+endif
+
+do Syntax xml
+syn spell toplevel
+syn cluster xmlTagHook add=rngTagName
+syn case match
+
+syn keyword rngTagName anyName attribute choice data define div contained
+syn keyword rngTagName element empty except externalRef grammar contained
+syn keyword rngTagName group include interleave list mixed name contained
+syn keyword rngTagName notAllowed nsName oneOrMore optional param contained
+syn keyword rngTagName parentRef ref start text value zeroOrMore contained
+
+hi def link rngTagName Statement
+
+let b:current_syntax = 'rng'
+
+endif