Standardize exit message

[k-doering-NOAA]

I noticed there are many variations on EXIT - see warning throughout the Stock Synthesis source code (for cases where SS3 exits early on error), including:

• fatal read error, see warning
• exit, see warning
• SS3 will exit, see warning
• exit see warning

It may be nice to clean these up so they always print the same message; perhaps we could even make a small function with the message, so it is easier to standardized the error and reduce the typing by a few keystrokes.

I wonder if this is something @nschindler-noaa would be interested in working on, if @Rick-Methot-NOAA thinks it is worth the time to do this? This seems low priority, but helpful, in my opinion.

[Rick-Methot-NOAA]

Seems like a fine suggestion.