update_properties updates the properties of the dash/trash

How convenient it would be to use update_properties to update the properties of a trash/dash

```ruby
class Person < Hashie::Dash
  property :name, required: true
  property :email
  property :occupation, default: 'Rubyist'
end

p = Person.new({name: 'alice', occupation: 'dolls'})
p.update_properties({name: 'greg'})
p.name #=> greg
p.occupation #=> Rubyist
``` 

if you like it, i'll udpate the changelog and the readme.
makes sens. 
What about aliasing the two methods, since it does basically the same job? 
Or you did mean rename assert_required_properties_set! in all the other places also?