health changes to red when below 50%
added a potion class. you can now press 'h' to heal but it is kinda buggy
updated potion.js.  it nows takes 2 arguments.  update keyboard control.js, now the health properly display (bug fix to earlier commit)
fixed the browser can't refresh issue
finalized the potion system. Potion now shows on the quickslot bar and you press 1 to use it.
changed potion to make sprite from potion.png directly like it was done for entity
refactored health bar code into entity
forgot to save combat.js
updated compiled js files
Merge branch 'add-health-display'

Conflicts:
	assets/tilesets/ui.json
	assets/tilesets/ui.png
	dist/dungeongeneration.js
	dist/dungeongeneration.min.js
	lib/gameobjects/systems/combat.js