Add Compiler reference via cpl attr in script tag

[Hernanm0g]

As @aczell described in PR #424, the lang attribute in <script> tag, causes some unwanted issues in vscode+vetur developer's experience. Aczell's solution works, so this PR is another way to solve the problem allowing a cpl attribute in script tag, for instance:

<script cpl="vuetify">

So vue-component will check for this cpl reference and, if exists, will look for a global.vue.lang.vuetify method, and will run it as a compiler.

This will help several developers, cause when you use <script lang="js">, it breaks: File autocomplete, syntax highlighting... and some weird warning pop up.

[ackzell]

Hey @Akryum,

I was wondering if this is something we could bring into the package or if you think there is an alternative approach we can take for the loader to work (I also created #424 as pointed out by @Hernanm0g)