* implemented directory zip download
* single html file page for Filer
* Filer allows uploads
* tree_patterner function to ease creation of website tree
* changed name and signature of BaseProvider.get_content() to handle_get
* a provider can now define handlers of any http method (POST, PUT, ...etc) by
defining handle_<method name> method in the subclass
* a provider can now define a default request handler method named
handle_default() to be called if no handler for the request method is
defined
* handler now will parse body if `content-type` header is
`multipart/form-data` and pass the data as dictionary to the provider
to the provider