[nvim] Add a gocsstmpl template

This is based on gotexttmpl and css highlighting.

config/nvim/syntax/gocsstmpl.vim

@@ -0,0 +1,17 @@
+if exists("b:current_syntax")
+  finish
+endif
+
+if !exists("g:main_syntax")
+  let g:main_syntax = 'css'
+endif
+
+runtime! syntax/gotexttmpl.vim
+runtime! syntax/css.vim
+unlet b:current_syntax
+
+syn cluster htmlPreproc add=gotplAction,goTplComment
+
+let b:current_syntax = "gocsstmpl"
+
+" vim: sw=2 ts=2 et