powerups added and next steps

-added powerups to randomly appear during spawnwave phase.
-added shotspawns to player to allow for improved weaponry
-picking up powerup adds 3 health to player and enables firing bolts
from additional shotspawns.  powerups are implemented as tiers. each
additional powerup that is picked up advances the player's firepower
capacity through use of a powerup counter tested by a switch statement.
-player health and current powerup tier is saved and passed to the next
levels

to implement next::
Currently the player has HP but only 1 life.  Let's give the player a
total of 3 lives to start.  When the player loses a life, the
powerup/weapon tier would drop by one.
Moreover, there should be a short phase in which the player resets and
momentarily receives no additional incoming damage.