Group `help` and `desc()` together before task definitions.

`help` and `desc()` work together to display help information for the
program, so grouping them together keeps the functionality colocated for
easier editing and debugging.

Also splitting out printing of desc strings into a separate function for
easier maintenance.
Group `help` and `tasks` together as 'Default Tasks'

These two tasks are general parts of the program structure, whereas the
other tasks are specific to this program. Therefore, group them as
default tasks that exist independently of the other, more specific
tasks.
Move main runner functionality to _main function at top of program

Since this functionality is part of the program's overall structure
rather than any individual task, grouping with the other structural
portions of the program.