support CoffeeTags on moon files

Hi @leafo:

I have been using [CoffeeTags](https://github.com/lukaszkorecki/coffeetags) a lot in my diary work. It clearly lists an outline of the coffeescript file, which saves me a lot time. 

Now I switched to moonscript projects, and found the CoffeeTags can work perfectly on moon files. So I combined the coffeetags vim plugin into the moonscript plugin. And now I can have a nice moonscript code outline in the tagbar.

![moontags](https://cloud.githubusercontent.com/assets/9838/3711034/be79955a-14ba-11e4-9d42-20bf131a7392.png)

@leafo : I assume it is. I haven't got a vim without ruby integration to check.  But I thinks that if statment is to make sure the client machine has got ruby env, since CoffeeTags is actually a ruby script.
Do you think we shall remove `echohl WarningMsg` to make sure the plugin won't be annoying on vim client without ruby? Please let me know. I can do that.