Gunkata early updates

This is the first round of updates to Gunkata since entering 1-Bit Jam.

• Revised title screen artwork with "start button" animation and start sound
• Targets randomly change after 5 seconds
• Moved the info message up several pixels to not obscure the player
• Fine tuning player responsiveness
• Changed player keyboard controls from Comma to Enter key
• New screenshots on game page
• Added Castlevania-style graphical ammo counter bar instead of a number
• Swapped order of clock timer and ammo counter in HUD