GraphML-Attributes support in GraphMLWriter

[ziodave]

Would it be possible to support GraphML-Attributes in GraphMLWriter?

GraphMLMetadata<T> could be have two new fields:

• String name
• Enum type

where the type Enum can be boolean, int, long, float, double, or string.

A new constructor could allow to set the above fields, otherwise null by default:

public GraphMLMetadata(String description, String default_value, Function<T, String> function, String name, Enum type)

The GraphMLWriter.writeKeySpecification method can be extended to support the 2 new fields.