add --vmrss-adjust-percent option for dynamic VMRSS adjustment

Fix Arch Linux package URL

New argument `--kill-wait` controls maximum time earlyoom waits for a killed process to exit

build(deps): bump actions/checkout from 2 to 6

Configurable wait timeout for process to end and `-w SECONDS` CLI option

kill: implement an option for trigger kernel oom killer

earlyoom.initscript.in: Append to log, don't overwrite

Implement -P to invoke a program as pre-hook before killing a process

fix: #341

Export EARLYOOM_ENVIRON of killed processes along with related info