Tidy the script startup code

[slowpeek]

Changes:

• $stages and $specified_arguments are arrays now (were strings).

Improvements:

• extra commands reside in $other_commands array. It is used both in valid commands check and in the 'unrecognized argument' error message. Previously they were listed literally in both places.
• easier to edit and more readable code producing the 'unrecognized argument' error message
• generic code cleanup

Btw I intentionally dont quote the left side in [[ $a == "$b" ]] conditions. It is not required in bash. As for zsh I refer to this piece from the docs:

Normal shell expansion is performed on the file, string and pattern arguments, but the result of each expansion is constrained to be a single word, similar to the effect of double quotes.

[slowpeek]

Are you sure you've read into the PR text and the code? The very first line says:

$stages and $specified_arguments are ARRAYS now (were strings).

Hence your objections are irrelevant.

Perhaps your bash is configured differently than the default? By default bash treats a string in quotes as a single parameter. Plus I'd like to preserve zsh compatibility.

You've got wrong every single word I've said.

[myspaghetti]

Did you forget to commit the change that made them into arrays?

[myspaghetti]

Oh would you look at that, they're arrays. Huh.

[slowpeek]

Oh would you look at that, they're arrays. Huh.

Haha, yeah. Thats what the PR message says.