split into multiple packages

[nsajko]

The goal of enumerating each well-known graph property and family conflicts with the goal of being a light-weight dependency. Even though this package does not have almost any executable code, defining a great number of new types could still be taxing on the compiler, I guess.

It might make sense to:

• Split up the abstract supertype from the definitions of particular properties. Then loading the abstract supertype would not imply loading all the properties.

• Split up some of the particular property definitions from some of the others. Then loading a single concrete property would not imply loading all properties.