Update v1.04:
Added:
Hard and Easy difficulty settings.
Different leaderboards for different difficulty settings
Option to see the user rank in leaderboards
Total kills display at level end screen

Bug Fixes: 
Controller setup in pause menu bug

Changes:
Updated achievements so that "Hard Boiled", "Just another day", "A master at my skill", "End of the week" and "Done and done!" can only be unlocked on medium difficulty