Implement generation attributes for enums and custom objects

v2.1.0

Implement generation attributes for enums and custom objects

Fix xml docs not getting produced for all target frameworks

v2.0.1

Update Chance.NET.csproj

Object generation attributes overhaul.

Same as what is described in the pre-release, with fixes to certain places where removing the null defaults caused problems.

Object generation attributes overhaul.

Restructured most of the generation method parameters to better reflect on their generated attribute definitions. Mostly required replacing all null default values that indicated the use of defaults with a non-null equivalent that was also described in the comments to produce the default behavior.

Also hid all static helper methods as they were semantically incorrect for the Chance class and added comment documentation wherever it was missing.