Patch v0.5.1

• Heavily cleaned up enemy knockback logic. These changes should make playing as Roxie much less annoying.
• Replaced the basic enemies in the cave area with rock reskins.
• Certain enemies (notably Bugs) no longer shoot when the player is within melee range.
• Certain enemies that move cardinally (notably Fish) stop in place more often and are less likely to wander off-screen.
• Astro's bullets now have slight shot speed variation.
• Adjusted the fire rate of various enemies (VERY slightly).
• Implemented some more (work in progress) sound effects.
• Hearts, pips, and ticks in the UI have a new visual effect when their respective values increase.
• Hearts in the UI no longer shake when the game is paused.
• Roxie no longer shakes when the game is paused.
• Removed irrelevant UI from the endless screen.
• Slightly adjusted the boss health bar position in the UI.
• Toned down various bullet particles.