To add a new vertical coordinate type:

1- Design the new table (on paper)
2- Modify the validity tables to include your new vcoord (e.g. ptop_8_valid)
3- Add elements to the structure (type grid_descriptor) if necessary
4- Add a branch to your new vcoord in the build constructor (new_build_vert)
5- Write the encoder for your new vcoord (e.g. encode_vert_5002)
6- Add support to your vcode in 
      fstd_init, new_from_table
7- Add get/put entries if the structure has been modified (step 3 above)
8- Generate a file that contains your new coordinate record
9- Add a branch to your new vcoord in the read constructor (new_read)
10- Write a decoder for your new vcoord (e.g. decode_vert_5002)
11- Add a level calculator (e.g. compute_pressure_5002)
12- Add a branch for your new vcoord in the printer (print_desc and print_vcode_description)
13- Add case statement in get_logical LOGP for new vcode
