Refactor: Use 'main' instead of 'data'.

Refactor: Use 'main' instead of 'data'.

The original goal of 'data' is to be used as the main store of data for the program.
A program using the programs as a library are also expected to get and use this structure.

The problem is that the programs are designed such that the caller to the program (as a library) should not have access to internal details.
Refactor 'data' to 'main'.
This is a more precise name in that it is the structure passed as if it were called from 'main(argc, argv)'.
This also frees up 'data' for internal use such that 'data' can now be the more generalized 'data' without exposing anything to 'main'.

The Controller program is already using 'main', so that 'main' was refactored to 'global'.

There are still more changes to do, such as restructuring the 'main' types to ensure nothing unwanted is exposed to a caller.
These additional changes, however, are beyond this scope of this commit.