Fits graphical models using kruskal's algorithm. At the moment it supports
- calculating raw edges for gaussian, discrete, and mixed cases.
- setting a threshold
- make secure with Principals and mechanisms https://www.securecoding.cert.org/confluence/pages/viewpage.action?pageId=637
- get working on parellel version.
- write documentation
- change ints to size_t
- make test for column assertion
- handle NA NaN and Inf
- test that discrete elements aren't unique!
- make tests for the above
- add model for degenerate gaussian
- parallel
- refacture threshold_init and threshold_initializer
- compare vanilla kruskal to
grapHD.