Changes

Steffens tuner fixer branch (#1041)

* Clubb ticket #1025: Implemented changes dealing with pdf_params%thl1/2 and wp2 floating point errors occurring in tuning runs. BIT_CHANGING
- Added command-line option -t/--tuner to compile.bash which enables the -DTUNER compiler flag.
- Added line to gfortran compilation config file to easily disable openMP
- Added a couple error messages and cleaned up some instances of error handling in src/error.F90, src/clubb_driver.F90, and src/CLUBB_core/advance_clubb_core_module.F90
- Added global constant wp2_max in src/CLUBB_core/constants_clubb.F90 which sets the upper bound for wp2
- In pdf_closure, added sanity checks for pdf_params%thl1/2 (>=190K, <=1000K)
- Added debug warning in src/CLUBB_core/advance_wp2_wp3_module.F90 when wp2 is clipped.
- Added wp2_sfc clipping in src/CLUBB_core/sfc_varnce_module.F90
- Added debug_level_check to NaN check in clubb_driver.F90
- Added mention of the new compiler option to the README