Deprecate g:vue_disable_pre_processors

It was superseded by g:vue_pre_processors (#133)

I could add a message if g:vue_disable_pre_processors is set, asking
people to update their config to the new variable, but I'd rather not
interrupt people's workflows.

Author: Adriaan Zonnenberg

readme.md

@@ -119,8 +119,8 @@ When checking for pre-processor languages, multiple syntax highlighting checks a
 let g:vue_pre_processors = ['pug', 'scss']
 ```
 
-Or alternatively, disable pre-processor languages altogether:
+To disable pre-processor languages altogether (only highlight HTML, JavaScript, and CSS):
 
 ```vim
-let g:vue_disable_pre_processors = 1
+let g:vue_pre_processors = []
 ```

syntax/vue.vim

@@ -6,6 +6,11 @@ if exists("b:current_syntax")
   finish
 endif
 
+" Convert deprecated variable to new one
+if exists('g:vue_disable_pre_processors') && g:vue_disable_pre_processors
+  let g:vue_pre_processors = []
+endif
+
 runtime! syntax/html.vim
 syntax clear htmlTagName
 syntax match htmlTagName contained "\<[a-zA-Z0-9:-]*\>"
@@ -59,20 +64,18 @@ for item in s:language_config
   let s:language_dict[item.lang] = item.args
 endfor
 
-if !exists("g:vue_disable_pre_processors") || !g:vue_disable_pre_processors
-  if exists("g:vue_pre_processors")
-    let pre_processors = g:vue_pre_processors
-  else
-    let pre_processors = map(copy(s:language_config), {k, v -> v.lang})
-  endif
-
-  for language in pre_processors
-    if has_key(s:language_dict, language)
-      call call("s:register_language", get(s:language_dict, language))
-    endif
-  endfor
+if exists("g:vue_pre_processors")
+  let pre_processors = g:vue_pre_processors
+else
+  let pre_processors = map(copy(s:language_config), {k, v -> v.lang})
 endif
 
+for language in pre_processors
+  if has_key(s:language_dict, language)
+    call call("s:register_language", get(s:language_dict, language))
+  endif
+endfor
+
 syn region  vueSurroundingTag   contained start=+<\(script\|style\|template\)+ end=+>+ fold contains=htmlTagN,htmlString,htmlArg,htmlValue,htmlTagError,htmlEvent
 syn keyword htmlSpecialTagName  contained template
 syn keyword htmlArg             contained scoped ts