Merge: Better Vim documentation on classes (with special attention to the doc of...

Calling Nitdoc() or Ctrl-D on the word `Container` will now display the following in the preview window.

~~~
# standard::Container[standard::Container::E]

A collection that contains only one item.

Used to pass arguments by reference.

Also used when one want to give a single element when a full
collection is expected

## Class hierarchy
* Direct super classes: Collection
* All super classes: Collection, Object
* Direct sub classes: ListNode
* All sub classes: ListNode

## Properties
+ count(item: E): Int  # How many occurrences of `item` are in the collection?
+ first: E  # Return the first item of the collection
+ has(item: E): Bool  # Is `item` in the collection ?
+ has_all(other: Collection[E]): Bool  # Does the collection contain at least each element of `other`?
+ has_exactly(other: Collection[E]): Bool  # Does the collection contain exactly all the elements of `other`?
+ has_only(item: E): Bool  # Is the collection contain only `item`?
+ is_empty: Bool  # Is there no item in the collection?
+ item: E  # The stored item
+ item=(item: E)  # The stored item
+ iterator: Iterator[E]  # Get a new iterator on the collection.
+ join(sep: Text): String  # Concatenate and separate each elements with `sep`.
+ length: Int  # Number of items in the collection.
+ rand: E  # Return a random element form the collection
+ to_a: Array[E]  # Build a new array from a collection
~~~

Pull-Request: #1197
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>