Merge pull request AppImage#650 from AppImage/TheAssassin/issue-563 Replace uname -p with uname -m where applicable

Cosmetic fix for message 

feature/usage 

Merge pull request AppImage#359 from orivej/build-debug Support debug build

Merge pull request AppImage#354 from darealshinji/patch-1 avoid unneeded if-statements, initializer fixes

Decrease verbosity, no false alarms 

Overwrite $APPIMAGE and $APPDIR if they already exist, closesAppImag……e#66

Revert "Added wizardless commands (pack and unpack)" and re-implement… … original solution; add USAGE

Update AppRun.c 

Update runtime.c