refactor: Simplify messaging, remove calls to os.Exit and log.Fatal

[TekWizely]

• Allows built-in cmds to be called even if runfile not found
  • Prints not found ERROR messsage
• Removes all os.Exit() calls
  • Modifies most code paths to pass exitCode up to main
  • Renames cmdExitCode => exitCode
• Removes all log.Fatal() calls
  • Replaced with log.Print(); return 1
• run with no args => custom message
  • Includes path to current runfile
  • Includes link to project homepage
• In Shebang mode, run-version includes link to project homepage
• run help => custom usage message
• Suppresses warnings on fmt.* calls
  • either via //noinspection or via , = fmt.*
• Simplifies messaging
  • Uses more lowercase messaging
  • Uses full uppercase for ERROR / WARNING
• Improves failed assert messaging
• Fixes bug: inverted nil check on os.Executable
• Renames //noinspection => //goland:noinspection
• Changes to appease the IntelliJ typo/grammar gods
• Renames occurrences of RunFile => Runfile