Additional labeling and clarifying of Goddard code, particularly renderer.c

[Tubular-Bells]

This pull request renames many Goddard functions and variables to be more descriptive. A few functions and variables do not have a discernible function, as they are only used as part of incomplete, unused functions. While I could have left these as-is, I took the liberty of giving them names anyway, if only for improving the human readability of the code. I have also added more UNUSED tags where appropriate. Lastly, some comments were left explaining the functionality of previously undocumented functions, at least where I felt reasonably confident I understood what the function was doing.

No changes to the behavior of the Goddard code have been made. In the case of gd_dl_rot_matrix (previously func_8019F2C4), minor changes to how the function uses its arguments have been made for the sake of clarity. gd_dl_rot_matrix is only called during a specific switch statement in the draw_shape function in draw_objects.c. Previously, the values 120, 121, and 122 were passed to represent the X, Y, and Z axes, respectively. Confusingly, 120 was then subtracted from this passed value in the function, meaning that it was essentially passing 0, 1, and 2 with extra steps. This change should have no effect on the behavior of the program.

This is by no means a comprehensive PR. Hopefully, further labeling will follow.

[gheskett]

These seem like good changes, obviously this code still needs a lot more cleanup but this is a good start.