start.sh: print warnings on unusual exit codes from the server process

[dktapps]

Introduction

This has been sitting idle on a branch for a couple of years. Not sure why it hasn't been merged as it looks basically fine as far as I can tell.

Changes

Behavioural changes

start.sh will now print warnings if the server experiences any of the following errors: SIGSEGV, SIGABRT, SIGKILL, any other anomalous exit code

Tests

Not tested, just found this while cleaning out old branches and thought it might be worth formally proposing

I tested this PR by doing the following (tick all that apply):

• Writing PHPUnit tests (commit these in the tests/phpunit folder)
• Playtesting using a Minecraft client (provide screenshots or a video)
• Writing a test plugin (provide the code and sample output)
• Other (provide details)

I don't know why this is still valid

[dktapps]

Sorry for the spam, just testing github actions