-Added inverse grav marker (default purple, same symbol as grav but rotated 180)

-Added sync dist into z buffer checks

-Fixed Z depth buffer error with short view distances (would show retrograde symbol in both directions)

Touchups to catch seamless being naughty

Added a missing heartbeat check on a texthudapi call

Switched to Text Hud API for symbol draws, stop info display, and menu

Adjusted render distance calc to hopefully not place symbols in the gap between camera frustrum and render range- this manifested as it only being visible on the screen edge.