Fix vertices

[jalving]

This pull request makes a few changes:

• update readme to point to the kahypar organization for download (as opposed to my fork)
• it adds wrappers for the new C interface functions
• it updates the Julia interface to use the new C interface functions. In summary, once the user sets fixed vertices, partitioning occurs using the the new C interface functions that expose the hypergraph object.
• added simple tests for fixed vertices
• made it possible to manually set the context config file in the Julia interface with a simple function
• updated build.jl to grab the binary build from commit 328760c

[SebastianSchlag]

Perfect! Thank you very much, Jordan!