Converted most fits to models with parameters, haven't done Tinker yet.
Finished Tinker functions
fixed bugs exposed by tests
Fixed MassFunction class to take new fitting_functions structure
Updated some docstrings for fitting functions (not done yet)
updated to match halomod, still some improvements to be made
made fit routines into class structure
fixed call signatures for fitting functions
finished making fit into class structure
added omegam_z and mean_dens_z
Merge branch 'fit_class'

* fit_class:
  added omegam_z and mean_dens_z
  finished making fit into class structure
  fixed call signatures for fitting functions
  made fit routines into class structure
  updated to match halomod, still some improvements to be made
  Updated some docstrings for fitting functions (not done yet)
  Fixed MassFunction class to take new fitting_functions structure
  fixed bugs exposed by tests
  Finished Tinker functions
  Converted most fits to models with parameters, haven't done Tinker yet.

Conflicts:
	hmf/hmf.py