added .gitignore file
major update with improvements, added comments, and removed errors

* f_rz was wrogly used in grid-cell averages of surface albedo
* added runoff and evap to state variables
* removed all local fields equivalent of surface_state variables (reduce redundancy)
* removed all local parameter with surface_param variables
* removed ITM and PDD approach for clarity (will be provisioned elsewhere in a different subroutine)

Version works for example/ and optimize/ directories (commits here will follow later on)
Update to latest version of 'surface_physics.f90'
Update to latest version of 'surface_physics.f90'