Updates

Hi @juvenn,
once again, thanks for adding me to the project, and sorry for the delay in bringing the initial updates.
I'm making a pull request with all the changes I added in my [fork/project here](https://github.com/bsutic/vim-mustache-handlebars) (I'll be closing that repo soon).

I was thinking this might be too much of a change at once for the project.. but I pushed anyway. We do not have to accept this - but it can be a good base for the discussion and further iteration. So let me know what you think!

Changes:
 - main change is switching to html filetype in [ftdetect](https://github.com/juvenn/mustache.vim/blob/updates/ftdetect/mustache.vim#L2).
What do you think of this?
In the meantime, I was studying vim-ruby plugin. They are also leaning heavily on html file type. Interestingly, for eruby files, but they set 'eruby' file type and [source html files](https://github.com/vim-ruby/vim-ruby/blob/master/ftplugin/eruby.vim#L51)
 - removed indent file - it is not needed when filetype is set to html
 - added better support for matchit
 - updated readme - this plugin is excellent for handlebars too (actually - I'm using it only for that file type :)

As I wrote above - lets discuss, comment and improve!