interior_point_fit: Interior point fit
In ant-stephenson/lhc: LHC Higgs Boson Classification Challenge

x contains lambda (dual var) as well

interior_point_fit(
  f,
  dualf,
  gradf,
  Hf,
  x,
  m,
  mu = 10,
  eps = 1e-06,
  eps_feas = 1e-06
)

`f`	objective function
`dualf`	dual objective function
`gradf`	residual vector
`Hf`	Hessian for residual
`x`	primal-dual point
`m`	number of inequality constraints
`mu`	interior-point step parameter
`eps`	tolerance for problem
`eps_feas`	tolerance for feasibility of primal-dual points