Hero GUI

Currently Displays a sprite for "Lives" portrait, draws the remaining
lives value to show the player how many they have left.

The health bar size scales based on the size of the player's current
maximum health, which can increase to a global cap of 40 (design
choice). Also, difficulty choices now modify the starting maximum health
value (default mode is 16 health), ranging from 8 to 20 Max Health.

Two healthbar draw codes are used, based on whether the player has over
30% health remaining. If the player has 30%+ health remaining, the bar
will be a solid green. Starting at 30%, a health bar is drawn that uses
the draw_healthbar color phasing. I set the healthbar drawing up this
way because the straight fading was ugly, and the straight color didn't
provide a 'low health' warning otherwise.

Lastly, the player currently has a "key_heal" that can be modified to
test health related things, or potentially energy related things if/when
implemented.