NEMO 3.6 to 3.7 migration guide

[mcastril]

After having to adapt our ORCA025 benchmark namelist to NEMO trunk version, we suggested to Claire to have a "migration guide" to make the move simpler to users and testers, most of all focused on people less familiarized with the latest changes.

I think it would be enough to make a list of the namelist parameters which substitute the precompilation keys that have been or will be removed, and maybe some other that have changed its default values in the reference namelist.

Here it is my preliminary list with the things I have found (mainly the ones that affected our config). I am also no entering in new namelist sections or features, but I put parameters which we had to add to our namelist_cfg because are mandatory (like the choice of a surface pressure method). I suppose those of you who are in charge of the simplification branch have already all this things in mind, so this is a very simple draft that you could improve easily:

Removed precompilation keys:

key_vvl
key_dynspg_ts
key_ldfslp
key_traldf_c2d
key_dynldf_c3d

Namelist attributes substituting precompilation keys:

ln_dynspg_exp
ln_dynspg_ts

Namelist attributes which have had a name edit:

ln_traldf_level -> ln_traldf_lev
ln_traldf_bilap -> ln_traldf_blp

ln_dynldf_level -> ln_dynldf_lev
ln_dynldf_bilap -> ln_dynldf_blp
rn_ahm_0_blp -> rn_bhm_0

ln_traadv_cen2 -> ln_traadv_cen

Namelist attributes which have changed its value in namelist_ref:

nn_stock (8640 -> 5475)
ln_clobber (false -> true)

ln_zps (true -> false)
ln_s_sh94 (true -> false)

ln_trabbc (true -> false)

ln_mle (true -> false)

ln_dynvor_een (true -> false)

TVD advection scheme was the default one, now it is needed to set one in namelist_cfg