Fix json version on travis
Travis: fix cwd before building
refactor likelihood models
Merge pull request #1200 from votjakovr/feature/gp_refactoring

refactor likelihood models
change default value of the derivative wrt hypers
Merge pull request #1201 from votjakovr/feature/gp_refactoring

change default value of the derivative wrt hypers
rational approximation using direct solvers added