Implement better compression for non-height terrain saves

[Son-Guhun]

#147

Further compression

Further compression can be achieved by iterating over all cells before generating the save string. If none of the cells have a height value, or all of them have the same height value, then this can be stored as the first information in the string, and then these cells can be saved using TV instead of TVHH, allowing us to fit 60 cells in a single string, instead of 30.

Eg:
#+g0g0h00ce2ece0c01080c040h00000000cece2e080c0g0g0c0h04080c08ce2ecec8000h0c0402010c0d0cccce2ec00c00080g00090904c8c8ce2ec1cc

The # as the first char indicates we are going to use a single height value for all the cells. The first two characters following the = represent the height value in the chosen base. The rest of the string is simply a TV string.