improve package scripts

[Razish]

We want to know if we've introduced assets that are not being packaged.
It should ignore gitignored and manually blacklisted files (e.g. the packaging scripts themselves).

We can take inspiration from CJK's gruggy shell script:

#!/usr/bin/env bash
# purpose: list files that are missing from the package script
set -euo pipefail

BLACKLIST=(
        ./package-files.txt
        ./package-find-missing.sh
        ./package.sh
        ./README.md
)

# FIXME: we can probably `return 1` instead of a dirty-flag break
file_is_blacklisted() {
        local needle="$1"
        match=0
        for bad_file in "${BLACKLIST[@]}"; do
                if [[ $bad_file = "$needle" ]]; then
                        match=1
                        break
                fi
        done
        [[ $match != 0 ]]
}

list_files() {
        while IFS='' read -r -d '' file; do
                if git check-ignore "$file" >/dev/null || file_is_blacklisted "$file"; then
                        echo >&2 "Ignoring $file"
                else
                        echo "$file"
                fi
        done < <(find ./* -type f -print0)
}

list_files | sort | git diff --no-index -- package-files.txt - # comm -13 package-files.txt -