Missing support for displayName property in the resources methods

[adamwojs]

Hi,

First of all thank you for this package. Works really great!

According to RAML specyfication is possible to set displayName property for the resources methods:

An alternate, human-friendly method name in the context of the resource. If the displayName node is not defined for a method, documentation tools SHOULD refer to the resource by its key, which acts as the method name.

(ref. https://github.com/raml-org/raml-spec/blob/1.0/versions/raml-10/raml-10.md#methods)

which seems to be not supported by this package.