Made `Makefile` install the level files under `/usr/share/games/nsnake/levels`
`Makefile` defines the system level dir and the game tells you to copy the level files from it to the local dir
Added `Utils::File::rm_f`
Updated the `Erase all Scores` option to include the level score files
Rewrote the string trimming functions - now they work with Windows line-endings too
Fixed bug where game crashed if we loaded level files made on Windows