Add more clarification around the different default types and when they apply in which context

[VasiliyLysokobylko]

The current RC1 version explains the different default types in section Shortcuts and Syntactic Sugar. In RC2 we should make sure that these are described a bit more clearly w/o using examples only.

There following rules need to be applied to determine the default type:

• If, and only if, a type declaration contains a properties node; the default type is object. For example (based on this rule):

types:
   Person:
      type: object
      properties:

can also be written

types:
   Person: 
      # default type is `object`, no need to explicitly define it
      properties:

• If, and only if, a type declaration does not contain either a properties node or no explicit type/schema node; the default type is always string. For example (based on this rule):

types:
   Person:
      properties:
         name: # no type or schema necessary since the default type is `string`

• The default type any is applied to any body node regardless if it is a response or request declaration that does not contain properties, types, or schema. That rule is necessary since the value of a body node has the same structure like a type declaration except that the key is always a media type. For example:

body:
  application/json: # key
    # default type is `any` 

The last rule is important for validation purposes and needs to be defined in the specification. Of course, each rule can be overridden by explicitly define a type. For example:

types:
   Person:
      properties:
         name: 
            type: number

[VasiliyLysokobylko]

https://github.com/raml-org/raml-spec/issues/325

[petrochenko-pavel-a]

This is already implemented