Document every method using YARD documentation tags

[subelsky]

I'd like us to have proper documentation for each method in Dim::Container. My preferred documentation system is YARD but I'm open to suggestions!

What I'm expecting is something like adding this line:

# Allows users to override a previously-defined dependency
# @param name [Symbol] name of the dependency to override
# @yieldreturn your block is expected to return the new value that replaces the old one
```ruby
    def override(name,&block)
      register(name,false,&block)
    end

With this in place the dim documentation will be easier to use.

Bonus: add a couple of examples to the documentation using @example tags