[To-do]: Implement non-regularized GGM

[AlexChristensen]

What do we need to do?
Add a version of {GGMnonreg}'s ggm_inference function to the package (see https://github.com/donaldRwilliams/GGMnonreg/blob/master/R/ggm_inference.R)

Is there a timeline to do it?
Before the end of February

What other functions would this to-do impact?
any and all EGA* functions
any and all network.* functions

[AlexChristensen]

Closing as implemented but stored in a branch: https://github.com/hfgolino/EGAnet/tree/nonreg-inference