Update: Improve signal handling code.

Update: Improve signal handling code.

Add a new line before printing the standard "Received signal code" message to ensure that it is always reasonably separated from the output being interrupted.

Simplify the verbosity variable check to a less than because the verbosity list is an enumeration.

Move the `fll_program_print_signal_received()` calls to the main program to help ensure consistent printing at the end of the program.
- Note: I am not certain if I want this instead in the main() function or not and I opted not to do so for now.

Fix some cases where the manual signal checks are still being performed to use the function instead.