Add --max-supercluster-size option

[TimD1]

Problem

• Supercluster size can blow up in regions with high-density variations, with no upper restrictions on size.
• This causes an explosion in required RAM and runtime, causing vcfdist to crash.
• There is no way to evaluate these regions.
• Relevant issues: command terminated by signal 9 #30 , Vcfdist requires too much memory when using VCF with SVs included #34

Solution

• Implement an option for restricting maximum supercluster size by providing a --max-supercluster-size parameter
• This can be used in combination with --cluster size 100 for fast clustering

To-Do

• implement supercluster splitting
• implement cluster splitting
• fix memory errors on small dataset
• fix bugs on small dataset
• fix bugs on 3 WGS datasets